Use of a supplemental promoter in conjunction with a carbon-supported, noble-metal-containing catalyst in liquid phase oxidation reactions

ABSTRACT

This invention relates to the use of a supplemental promoter in conjunction with a noble-metal-containing catalyst comprising a carbon support in catalyzing liquid phase oxidation reactions, a process for making of an improved catalyst comprising such a supplemental promoter, and an improved catalyst comprising such a supplemental promoter. In a particularly preferred embodiment, a supplemental promoter (most preferably bismuth or tellurium) is used in conjunction with a noble-metal-containing catalyst comprising a carbon support in a liquid phase oxidation process wherein N-(phosphonomethyl)iminodiacetic acid (i.e., “PMIDA”) or a salt thereof is oxidized to form N-(phosphonomethyl)glycine (i.e., “glyphosate”) or a salt thereof. The benefits of such a process include increased oxidation of the formaldehyde and formic acid by-products, and, consequently, decreased final concentrations of those by-products as well as other undesirable by-products, most notably N-methyl-N-(phosphonomethyl)glycine (i.e., “NMG”).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/208,686, filed Aug. 22, 2005, which is a divisional of U.S. patentapplication Ser. No. 10/427,830, filed May 1, 2003, now U.S. Pat. No.6,963,009, which is a divisional of U.S. patent application Ser. No.09/746,186, filed Dec. 21, 2000, now U.S. Pat. No. 6,586,621, whichclaims the benefit of U.S. Provisional Patent Application Ser. No.60/171,313 filed Dec. 21, 1999. The entire texts of U.S. patentapplication Ser. No. 09/746,186 and U.S. Provisional Patent ApplicationSer. No. 60/171,313 are incorporated herein by reference.

FIELD OF THE INVENTION

This invention generally relates to liquid phase oxidation processesusing a carbon-supported, noble-metal-containing catalyst (particularlya deeply reduced catalyst) in conjunction with a supplemental promoter(e.g., bismuth or tellurium). In an especially preferred embodiment,this invention relates to such a process whereinN-(phosphonomethyl)iminodiacetic acid (“PMIDA”) or a salt thereof isoxidized to form N-(phosphonomethyl)glycine (also known in theagricultural chemical industry as “glyphosate”) or a salt thereof. Thisinvention also generally relates to enhancing the activity, selectivity,and/or stability of a carbon-supported, noble-metal-containing catalyst(particularly a deeply reduced catalyst) using a supplemental promoter.

BACKGROUND OF THE INVENTION

N-(phosphonomethyl)glycine is described in Franz, U.S. Pat. No.3,799,758. N-(phosphonomethyl)glycine and its salts are convenientlyapplied as a post-emergent herbicide in an aqueous formulation.Glyphosate is a highly effective and commercially importantbroad-spectrum herbicide useful in killing or controlling the growth ofa wide variety of plants, including germinating seeds, emergingseedlings, maturing and established woody and herbaceous vegetation, andaquatic plants.

Various methods for making N-(phosphonomethyl)glycine are known in theart. Franz (U.S. Pat. No. 3,950,402) discloses thatN-(phosphonomethyl)glycine may be prepared by the liquid phase oxidativecleavage of PMIDA with oxygen in the presence of a catalyst comprising anoble metal deposited on the surface of an activated carbon support:

Other by-products also typically form, such as formic acid (HCO₂H),which is formed by the oxidation of the formaldehyde by-product; andaminomethylphosphonic acid (“AMPA”), which is formed by the oxidation ofN-(phosphonomethyl)glycine. Even though the Franz method produces anacceptable yield and purity of N-(phosphonomethyl)glycine, high lossesof the costly noble metal into the reaction solution (i.e., “leaching”)result because, under the oxidation conditions of the reaction, some ofthe noble metal is oxidized into a more soluble form, and both PMIDA andN-(phosphonomethyl)glycine act as ligands which solubilize the noblemetal.

In U.S. Pat. No. 3,969,398, Hershman discloses that activated carbonalone, without the presence of a noble metal, may be used to effect theoxidative cleavage of PMIDA to form N-(phosphonomethyl)glycine. In U.S.Pat. No. 4,624,937, Chou further discloses that the activity of thecarbon catalyst disclosed by Hershman may be increased by removing theoxides from the surface of the carbon catalyst before using it in theoxidation reaction. See also, U.S. Pat. No. 4,696,772, which provides aseparate discussion by Chou regarding increasing the activity of thecarbon catalyst by removing oxides from the surface of the carboncatalyst. Although these processes obviously do not suffer from noblemetal leaching, they do tend to produce greater concentrations of formicacid and formaldehyde by-product when used to effect the oxidativecleavage of N-(phosphonomethyl)iminodiacetic acid. These byproducts areparticularly undesirable because they react withN-(phosphonomethyl)glycine to produce unwanted by-products (mainlyN-methyl-N-(phosphonomethyl)glycine, sometimes referred to as “NMG”)which reduce the N-(phosphonomethyl)glycine yield. In addition, theformaldehyde by-product itself is undesirable because of its potentialtoxicity. See Smith, U.S. Pat. No. 5,606,107.

Optimally, therefore, it has been suggested that the formic acid andformaldehyde be simultaneously oxidized to carbon dioxide and water asthe PMIDA is oxidized to N-(phosphonomethyl)glycine in a single reactor,thus giving the following net reaction:

As the above references suggest, such a process requires the presence ofboth carbon (which primarily effects the oxidation of PMIDA to formN-(phosphonomethyl)glycine and formaldehyde) and a noble metal (whichprimarily effects the oxidation of formaldehyde and formic acid to formcarbon dioxide and water). Previous attempts to develop a stablecatalyst for such an oxidation process, however, have not been entirelysatisfactory.

Like Franz, Ramon et al. (U.S. Pat. No. 5,179,228) disclose using anoble metal deposited on the surface of a carbon support. To reduce theproblem of leaching (which Ramon et al. report to be as great as 30%noble metal loss per cycle), however, Ramon et al. disclose flushing thereaction mixture with nitrogen under pressure after the oxidationreaction is completed to cause re-deposition of the noble metal onto thesurface of the carbon support. According to Ramon et al., nitrogenflushing reduces the noble metal loss to less than 1%. Still, the amountof noble metal loss incurred with this method is unacceptable. Inaddition, re-depositing the noble metal can lead to loss of noble metalsurface area which, in turn, decreases the activity of the catalyst.

Using a different approach, Felthouse (U.S. Pat. No. 4,582,650)discloses using two catalysts: (i) an activated carbon to effect theoxidation of PMIDA into N-(phosphonomethyl)glycine, and (ii) aco-catalyst to concurrently effect the oxidation of formaldehyde intocarbon dioxide and water. The co-catalyst consists of an aluminosilicatesupport having a noble metal located within its pores. The pores aresized to exclude N-(phosphonomethyl)glycine and thereby prevent thenoble metal of the co-catalyst from being poisoned byN-(phosphonomethyl)glycine. According to Felthouse, use of these twocatalysts together allows for the simultaneous oxidation of PMIDA toN-(phosphonomethyl)glycine and of formaldehyde to carbon dioxide andwater. This approach, however, suffers from several disadvantages: (1)it is difficult to recover the costly noble metal from thealuminosilicate support for re-use; (2) it is difficult to design thetwo catalysts so that the rates between them are matched; and (3) thecarbon support, which has no noble metal deposited on its surface, tendsto deactivate at a rate which can exceed 10% per cycle.

In PCT/US99/03402, Ebner et al. disclose a reaction process for makingN-(phosphonomethyl)glycine compounds from PMIDA compounds using a deeplyreduced, carbon-supported, noble metal catalyst which exhibits improvedresistance to noble metal leaching and increased destruction ofundesirable byproducts (e.g., formaldehyde). Still, this reactionprocess typically does not eliminate all the formaldehyde and formicacid byproduct, and, consequently, also does not eliminate all theN-methyl-N-(phosphonomethyl)glycine byproduct.

Thus, a need continues to exist for an improved reaction process foroxidizing PMIDA to N-(phosphonomethyl)glycine using a catalyst whichexhibits resistance to noble metal leaching and increased oxidation offormic acid and formaldehyde into carbon dioxide and water (i.e.,increased formic acid and formaldehyde activity).

SUMMARY OF THE INVENTION

This invention provides, in part, for an improved process for oxidizingPMIDA, salts of PMIDA, and esters of PMIDA to formN-(phosphonomethyl)glycine, salts of N-(phosphonomethyl)glycine, andesters of N-(phosphonomethyl)glycine, particularly such a process whichuses a catalyst (or catalyst system) that (a) exhibits resistance tonoble metal leaching, and (b) exhibits increased oxidation of formicacid and/or formaldehyde, and consequent decreased formation of NMG; animproved process for oxidizing a substrate in general wherein theactivity, selectivity, and/or stability of a carbon-supported,noble-metal-containing catalyst used to catalyze the oxidation isenhanced by merely mixing the catalyst with a supplemental promoter(rather than using a catalyst which already contains the promoter, and,consequently, is more costly to manufacture); an improved process formaking an oxidation catalyst system (particularly an oxidation catalystsystem for oxidizing PMIDA compounds) having enhanced activity,selectivity, and/or stability; and an oxidation catalyst system(particularly an oxidation catalyst system for oxidizing PMIDAcompounds) having enhanced activity, selectivity, and/or stability.

Briefly, therefore, the present invention is directed to a process foroxidizing formic acid or formaldehyde in the presence of a catalyst anda supplemental promoter. Here, the catalyst comprises a noble metal anda carbon support; and the mass ratio of the supplemental promoter to thecatalyst is at least about 1:15,000.

The present invention is also directed to a process for oxidizing asubstrate in general using a catalyst comprising a carbon support and anoble metal. In this embodiment, the process comprises contacting thesubstrate with oxygen in the presence of the catalyst and a supplementalpromoter. Here, the mass ratio of the supplemental promoter to thecatalyst is at least about 1:15,000. And, before the catalyst is used inthe oxidation of the substrate, the catalyst:

-   -   A. comprises a non-graphitic carbon support having a noble metal        at a surface of the non-graphitic carbon support; and        -   is identifiable as yielding no greater than about 0.7 mmole            of carbon monoxide per gram of catalyst when a dry sample of            the catalyst in a helium atmosphere is heated from about 20°            to about 900° C. at a rate of about 10° C. per minute, and            then at about 900° C. for about 30 minutes; or    -   B. comprises a non-graphitic carbon support having a noble metal        and a catalyst-surface promoter at a surface of the        non-graphitic carbon support; and        -   is identifiable as yielding no greater than about 0.7 mmole            of carbon monoxide per gram of catalyst when a dry sample of            the catalyst, after being heated at a temperature of about            500° C. for about 1 hour in a hydrogen atmosphere and before            being exposed to an oxidant following the heating in the            hydrogen atmosphere, is heated in a helium atmosphere from            about 20° to about 900° C. at a rate of about 10° C. per            minute, and then at about 900° C. for about 30 minutes; or    -   C. comprises a non-graphitic carbon support having a noble        metal, carbon, and oxygen at a surface of the non-graphitic        carbon support, the ratio of carbon atoms to oxygen atoms at the        surface being at least about 30:1, as measured by x-ray        photoelectron spectroscopy; or    -   D. comprises a non-graphitic carbon support having a noble        metal, a catalyst-surface promoter, carbon, and oxygen at a        surface of the non-graphitic carbon support; and        -   is identifiable as having a ratio of carbon atoms to oxygen            atoms at the surface which is at least about 30:1, as            measured by x-ray photoelectron spectroscopy after the            catalyst is heated at a temperature of about 500° C. for            about 1 hour in a hydrogen atmosphere and before the            catalyst is exposed to an oxidant following the heating in            the hydrogen atmosphere; or    -   E. comprises a non-graphitic carbon support having (i) a noble        metal at a surface of the non-graphitic carbon support; and (ii)        a surface layer having a thickness of about 50 Å as measured        inwardly from the surface and comprising oxygen and carbon, the        ratio of carbon atoms to oxygen atoms in the surface layer being        at least about 30:1, as measured by x-ray photoelectron        spectroscopy; or    -   F. comprises a non-graphitic carbon support having: (a) a noble        metal and a catalyst-surface promoter at a surface of the        non-graphitic carbon support; and (b) a surface layer having a        thickness of about 50 Å as measured inwardly from the surface        and comprising carbon and oxygen; and        -   is identifiable as having a ratio of carbon atoms to oxygen            atoms in the surface layer of at least about 30:1, as            measured by x-ray photoelectron spectroscopy after the            catalyst is heated at a temperature of about 500° C. for            about 1 hour in a hydrogen atmosphere and before the            catalyst is exposed to an oxidant following the heating in            the hydrogen atmosphere;    -   G. is formed by a process comprising depositing a noble metal at        a surface of a non-graphitic carbon support, and then heating        the surface at a temperature of at least about 400° C., wherein,        before the noble metal deposition, the ratio of carbon atoms to        oxygen atoms at the surface of the non-graphitic carbon support        is at least about 20:1, as measured by x-ray photoelectron        spectroscopy; or    -   H. is formed by a process comprising depositing a noble metal at        a surface of a carbon support, and then exposing the surface to        a reducing environment, wherein, before the noble metal        deposition, the carbon support has carbon atoms and oxygen atoms        at the surface of the carbon support in amounts such that the        ratio of carbon atoms to oxygen atoms at the surface is at least        about 20:1, as measured by x-ray photoelectron spectroscopy; or    -   I. is formed by a process comprising depositing a noble metal at        a surface of a non-graphitic carbon support, and then heating        the surface at a temperature greater than about 500° C.

The present invention is also directed to a process for making anoxidation catalyst system.

In one embodiment directed to a process for making an oxidation catalystsystem, the process comprises mixing a noble-metal-containing catalystwith a supplemental promoter in the presence of formic acid orformaldehyde. Here, the noble-metal-containing catalyst comprises anoble metal and a carbon support; and the mass ratio of the supplementalpromoter to the noble-metal-containing catalyst is at least about1:15,000.

In another embodiment directed to a process for making an oxidationcatalyst system, the catalyst system is prepared using a carbon supporthaving carbon atoms and oxygen atoms at a surface of the non-graphiticcarbon support. In this process, a noble metal is deposited at thesurface of the carbon support to form a noble-metal-containing catalyst.Oxygen-containing functional groups are subsequently removed from thesurface of the noble-metal-containing catalyst to form anoble-metal-containing catalyst comprising a deoxygenated surface. Thisremoval of oxygen-containing functional groups comprises:

-   -   (i) heating the surface of the noble-metal-containing catalyst        at a temperature of greater than about 500° C.; or    -   (ii) heating the surface of the noble-metal-containing catalyst        at a temperature of at least about 400° C., wherein, before the        noble metal deposition, the ratio of carbon atoms to oxygen        atoms at the surface of the non-graphitic carbon support is at        least about 20:1, as measured by x-ray photoelectron        spectroscopy; or    -   (iii) exposing the surface of the noble-metal-containing        catalyst to a reducing environment, wherein, before the noble        metal deposition, the ratio of carbon atoms to oxygen atoms at        the surface of the non-graphitic carbon support is at least        about 20:1, as measured by x-ray photoelectron spectroscopy; or    -   (iv) exposing the surface of the noble-metal-containing catalyst        to a reducing environment so that the ratio of carbon atoms to        oxygen atoms at the deoxygenated surface of the        noble-metal-containing catalyst comprising the deoxygenated        surface is at least about 30:1, as measured by x-ray        photoelectron spectroscopy; or    -   (v) exposing the surface of the noble-metal-containing catalyst        to a reducing environment so that no greater than about 0.7        mmole of carbon monoxide per gram of the noble-metal-containing        catalyst comprising the deoxygenated surface desorb from the        deoxygenated surface when a dry sample of the        noble-metal-containing catalyst comprising the deoxygenated        surface is heated in a helium atmosphere from about 20° to about        900° C. at a rate of about 10° C. per minute, and then at about        900° C. for about 30 minutes.

After removing oxygen-containing functional groups from the surface ofthe noble-metal-containing catalyst, the noble-metal-containing catalystis mixed with a supplemental promoter. Here, the mass ratio of thesupplemental promoter to the noble-metal-containing catalyst is at leastabout 1:15,000.

This invention is also directed to an oxidation catalyst system.

In one embodiment directed to an oxidation catalyst system, theoxidation catalyst system is prepared by a process comprising mixing anoble-metal-containing catalyst with a supplemental promoter in thepresence of formic acid or formaldehyde. Here, thenoble-metal-containing catalyst comprises a noble metal and a carbonsupport; and the mass ratio of the supplemental promoter to thenoble-metal-containing catalyst is at least about 1:15,000.

In another embodiment directed to an oxidation catalyst system, theoxidation catalyst system is prepared using a carbon support. Whenpreparing this catalyst system, a noble metal is deposited onto asurface of the carbon support to form a noble-metal-containing catalyst.Oxygen-containing functional groups are subsequently removed from thesurface of the noble-metal-containing catalyst to form anoble-metal-containing catalyst comprising a deoxygenated surface. Thisremoval of oxygen-containing functional groups comprises:

-   -   (i) heating the surface of the noble-metal-containing catalyst        at a temperature of greater than about 500° C.; or    -   (ii) heating the surface of the noble-metal-containing catalyst        at a temperature of at least about 400° C., wherein, before the        noble metal deposition, the non-graphitic carbon support has        carbon atoms and oxygen atoms at the surface in amounts such        that the ratio of carbon atoms to oxygen atoms at the surface is        at least about 20:1, as measured by x-ray photoelectron        spectroscopy; or    -   (iii) exposing the surface of the noble-metal-containing        catalyst to a reducing environment, wherein, before the noble        metal deposition, the non-graphitic carbon support has carbon        atoms and oxygen atoms at the surface in amounts such that the        ratio of carbon atoms to oxygen atoms at the surface is at least        about 20:1, as measured by x-ray photoelectron spectroscopy; or    -   (iv) exposing the surface of the noble-metal-containing catalyst        to a reducing environment so that the ratio of carbon atoms to        oxygen atoms at the deoxygenated surface of the        noble-metal-containing catalyst comprising the deoxygenated        surface is at least about 30:1, as measured by x-ray        photoelectron spectroscopy; or    -   (v) exposing the surface of the noble-metal-containing catalyst        to a reducing environment so that no greater than about 0.7        mmole of carbon monoxide per gram of the noble-metal-containing        catalyst comprising the deoxygenated carbon support surface        desorb from the deoxygenated surface when a dry sample of the        noble-metal-containing catalyst comprising the deoxygenated        surface is heated in a helium atmosphere from about 20° to about        900° C. at a rate of about 10° C. per minute, and then at about        900° C. for about 30 minutes.        After oxygen-containing functional groups have been removed from        the surface of the noble-metal-containing catalyst, the        noble-metal-containing catalyst is mixed with a supplemental        promoter. Here, the mass ratio of the supplemental promoter to        the noble-metal-containing catalyst is at least about 1:15,000.

This invention also is directed to a general process for makingN-(phosphonomethyl)glycine, a salt of N-(phosphonomethyl)glycine, or anester of N-(phosphonomethyl)glycine. This process comprises oxidizingN-(phosphonomethyl)iminodiacetic acid, a salt ofN-(phosphonomethyl)iminodiacetic acid, or an ester ofN-(phosphonomethyl)iminodiacetic acid in the presence of an oxidationcatalyst. Before the oxidation, this oxidation catalyst:

-   -   A. comprises a carbon support having a noble metal at a surface        of the carbon support; and        -   is identifiable as yielding no greater than about 1.2 mmole            of carbon monoxide per gram of catalyst when a dry sample of            the catalyst in a helium atmosphere is heated from about 20°            to about 900° C. at a rate of about 10° C. per minute, and            then at about 900° C. for about 30 minutes; or    -   B. comprises a carbon support having a noble metal, carbon, and        oxygen at a surface of the carbon support, the ratio of carbon        atoms to oxygen atoms at the surface being at least about 20:1,        as measured by x-ray photoelectron spectroscopy; or    -   C. comprises a carbon support comprising: (a) a noble metal at a        surface of the carbon support; and (b) a surface layer having a        thickness of about 50 Å as measured inwardly from the surface        and comprising carbon and oxygen, the ratio of carbon atoms to        oxygen atoms in the surface layer being at least about 20:1, as        measured by x-ray photoelectron spectroscopy; or    -   D. is formed by a process comprising depositing a noble metal at        a surface of a carbon support, and then heating the surface at a        temperature of at least about 400° C.; or    -   E. is formed by a process comprising: depositing a noble metal        at a surface of a carbon support, and then exposing the surface        to a reducing environment, wherein, before the noble metal        deposition, the carbon support has carbon atoms and oxygen atoms        at the surface in amounts such that the ratio of carbon atoms to        oxygen atoms at the surface is at least about 20:1, as measured        by x-ray photoelectron spectroscopy; or    -   F. comprises a carbon support having a noble metal, a promoter,        carbon, and oxygen at a surface of the carbon support; or    -   G. comprises a carbon support having: (a) a noble metal and a        promoter at a surface of the carbon support; and (b) a surface        layer having a thickness of about 50 Å as measured inwardly from        the surface and comprising carbon and oxygen, the catalyst being        identifiable as having a ratio of carbon atoms to oxygen atoms        in the surface layer which is at least about 20:1, as measured        by x-ray photoelectron spectroscopy after the catalyst is heated        at a temperature of about 500° C. for about 1 hour in a hydrogen        atmosphere and before the catalyst is exposed to an oxidant        following the heating in the hydrogen atmosphere.

Other features of this invention will be in part apparent and in partpointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one example of a batch-reaction embodiment that may be usedin accordance with this invention.

FIG. 2 shows one example of an embodiment that may be used in accordancewith this invention for the oxidation of formic acid or formaldehydecontained in an aqueous waste stream generated from the oxidation ofN-(phosphonomethyl)iminodiacetic acid for preparingN-(phosphonomethyl)glycine.

FIG. 3 shows the effect on the formic acid byproduct concentrationprofile over 20 reaction runs caused by a one-time introduction ofbismuth oxide directly into a PMIDA oxidation reaction mixture. Here,the catalyst concentration in the reaction mixture was 0.5% by weight,and the catalyst contained 5% by weight platinum and 0.5% by weightiron.

FIG. 4 shows the effect on the formic acid byproduct concentrationprofile over 30 reaction runs caused by a one-time introduction ofbismuth oxide directly into a PMIDA oxidation reaction mixture. Here,the catalyst concentration in the reaction mixture was 0.75% by weight,and the catalyst contained 5% by weight platinum and 1% by weight tin.

FIG. 5 shows the effect on the formaldehyde byproduct concentrationprofile over 30 reaction runs caused by a one-time introduction ofbismuth oxide directly into a PMIDA oxidation reaction mixture. Here,the catalyst concentration in the reaction mixture was 0.75% by weight,and the catalyst contained 5% by weight platinum and 1% by weight tin.

FIG. 6 shows the effect on the NMG byproduct concentration profile over30 reaction runs caused by a one-time introduction of bismuth oxidedirectly into a PMIDA oxidation reaction mixture. Here, the catalystconcentration in the reaction mixture was 0.75% by weight, and thecatalyst contained 5% by weight platinum and 1% by weight tin.

FIG. 7 shows the effect on formic acid, formaldehyde, and NMG productionduring a PMIDA oxidation reaction caused by mixing bismuth oxide with anoxidation catalyst that had been used in 133 previous batch PMIDAoxidation reactions. Here, the catalyst comprised 5% by weight platinumand 0.5% by weight iron on a carbon support.

FIG. 8 shows the effect on formic acid, formaldehyde, and NMG productionduring a PMIDA oxidation reaction caused by mixing bismuth oxide with anoxidation catalyst that had been used in 30 previous batch PMIDAoxidation reactions. Here, the catalyst comprised 5% by weight platinumand 1% by weight tin on a carbon support.

FIG. 9 shows the effect on the formic acid byproduct concentrationprofile over 107 reaction runs caused by a one-time mixing of bismuthoxide with a catalyst containing 5% by weight platinum and 1% by weighttin.

FIG. 10 shows the effect on the formaldehyde byproduct concentrationprofile over 107 reaction runs caused by a one-time mixing of bismuthoxide with a catalyst containing 5% by weight platinum and 1% by weighttin.

FIG. 11 shows the effect on the NMG byproduct concentration profile over107 reaction runs caused by a one-time mixing of bismuth oxide with acatalyst containing 5% by weight platinum and 1% by weight tin.

FIG. 12 shows the effect of two supplemental promoters by a comparisonof N-(phosphonomethyl) iminodiacetic acid oxidation rates when bismuthversus bismuth and tellurium are used as supplemental promoters.

FIG. 13 shows the effect of using two supplemental promoters by acomparison of the amount of platinum leached from the catalyst whenbismuth versus bismuth and tellurium are used as supplemental promoters.

FIG. 14 shows the effect of a supplemental promoter in oxidizing anaqueous stream of formic acid and formaldehyde by a comparison of formicacid oxidation activity when bismuth is used as a supplemental promoter.

FIG. 15 shows the effect of a supplemental promoter in oxidizing anaqueous stream of formic acid and formaldehyde by a comparison offormaldehyde oxidation activity when bismuth is used as a supplementalpromoter.

FIG. 16 shows the effect of a supplemental promoter in oxidizing anaqueous stream of formic acid and formaldehyde by a comparison of formicacid oxidation activity when tellurium is used as a supplementalpromoter.

FIG. 17 shows the effect of a supplemental promoter in oxidizing anaqueous stream of formic acid and formaldehyde by a comparison offormaldehyde oxidation activity when tellurium is used as a supplementalpromoter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A. The OxidationCatalyst

The catalyst used in the present invention may be used to catalyzeliquid phase (i.e., in an aqueous solution or an organic solvent)oxidation reactions, especially in acidic oxidative environments and inthe presence of solvents, reactants, intermediates, or products whichsolubilize noble metals. The catalyst exhibits resistance to noble metalleaching from the catalyst surface under these conditions.

The noble metal component of the catalyst serves various functions. Forexample, depositing a noble metal onto the surface of a catalystconsisting of a carbon support alone tends to reduce the rate ofdeactivation of the catalyst. To illustrate, whenN-(phosphonomethyl)glycine is prepared by the liquid phase oxidativecleavage of PMIDA with oxygen in the presence of a catalyst consistingof an activated carbon support without a noble metal, the activatedcarbon is found to deactivate as much as 10% per cycle or more. Withoutbeing bound by any particular theory, it is believed that thedeactivation of the activated carbon arises because the surface of thecarbon support oxidizes under the reaction conditions. See Chou, U.S.Pat. No. 4,624,937. See also, Chou, U.S. Pat. No. 4,696,772, whichprovides a separate discussion related to deactivation of activatedcarbon by oxidation of the surface of the carbon. In the presence of thenoble metal, however, the rate of deactivation of the activated carbonis diminished. It is believed that the noble metal can react with theoxidant at a faster rate than the activated carbon surface, and, thus,preferentially removes the oxidant from solution before extensiveoxidation of the carbon surface can occur. Further, unlike many oxidespecies which form at activated carbon surfaces and require hightemperature treatments to be reduced, oxide species which form at thesurface of a noble metal typically are easily reduced by the reducingagents present in or added to the reaction mixture (e.g., the aminefragment cleaved, formaldehyde, formic acid, H₂, etc.), thus restoringthe noble metal surface to a reduced state. In this manner, the catalystof this invention advantageously exhibits significantly longer life aslong as the noble metal is not lost by leaching, or sintered (i.e., inthe form of undesirably thick layers or clumps) by processes such asdissolution and re-deposition or noble metal agglomeration.

Also, depending on the particular oxidation reaction, a noble metal maybe more effective than carbon at effecting the oxidation. For example,in the context of the oxidative cleavage of PMIDA to formN-(phosphonomethyl)glycine, although a carbon catalyst can be used inthe oxidation of PMIDA to N-(phosphonomethyl)glycine, it is the noblemetal component that primarily effects the oxidation of the undesirableformaldehyde and formic acid by-products into the more preferredby-products, carbon dioxide and water.

Oxygen-containing functional groups (e.g., carboxylic acids, ethers,alcohols, aldehydes, lactones, ketones, esters, amine oxides, andamides) at the surface of the carbon support tend to increase noblemetal leaching and potentially increase noble metal sintering duringliquid phase oxidation reactions, and, thus, reduce the ability of thecatalyst to oxidize oxidizable substrates, particularly formaldehyde andformic acid during the PMIDA oxidation reaction. As used herein, anoxygen-containing functional group is “at the surface of the carbonsupport” if it is bound to an atom of the carbon support and is able tochemically or physically interact with compositions within the reactionmixture or with the metal atoms deposited on the carbon support.

Many of the oxygen-containing functional groups that reduce noble metalresistance to leaching and sintering and reduce the activity of thecatalyst desorb from the carbon support as carbon monoxide when thecatalyst is heated at a high temperature (e.g., 900° C.) in an inertatmosphere (e.g., helium or argon). Thus, measuring the amount of COdesorption from a fresh catalyst (i.e., a catalyst that has notpreviously been used in a liquid phase oxidation reaction) under hightemperatures is one method that may be used to analyze the surface ofthe catalyst to predict noble metal retention and maintenance ofcatalyst activity. One way to measure CO desorption is by usingthermogravimetric analysis with in-line mass spectroscopy (“TGA-MS”).Preferably, no greater than about 1.2 mmole of carbon monoxide per gramof catalyst desorb from the catalyst when a dry, fresh sample of thecatalyst in a helium atmosphere is subjected to a temperature which isincreased from about 20° to about 900° C. at about 10° C. per minute,and then held constant at about 900° C. for about 30 minutes. Morepreferably, no greater than about 0.7 mmole of carbon monoxide per gramof fresh catalyst desorb under those conditions, even more preferably nogreater than about 0.5 mmole of carbon monoxide per gram of freshcatalyst desorb, and most preferably no greater than about 0.3 mmole ofcarbon monoxide per gram of fresh catalyst desorb. A catalyst isconsidered “dry” when the catalyst has a moisture content of less than1% by weight. Typically, a catalyst may be dried by placing it into a N₂purged vacuum of about 25 inches of Hg at a temperature of about 120° C.for about 16 hours.

Measuring the number of oxygen atoms at the surface of a fresh catalystsupport is another method which may be used to analyze the catalyst topredict noble metal retention and maintenance of catalytic activity.Using, for example, x-ray photoelectron spectroscopy, a surface layer ofthe support which is about 50 Å in thickness is analyzed. Presentlyavailable equipment used for x-ray photoelectron spectroscopy typicallyis accurate to within ±20%. Typically, a ratio of carbon atoms to oxygenatoms at the surface (as measured by presently available equipment forx-ray photoelectron spectroscopy) of at least about 20:1 (carbonatoms:oxygen atoms) is suitable. Preferably, however, the ratio is atleast about 30:1, more preferably at least about 40:1, even morepreferably at least about 50:1, and most preferably at least about 60:1.In addition, the ratio of oxygen atoms to metal atoms at the surface(again, as measured by presently available equipment for x-rayphotoelectron spectroscopy) preferably is less than about 8:1 (oxygenatoms:metal atoms). More preferably, the ratio is less than 7:1, evenmore preferably less than about 6:1, and most preferably less than about5:1.

In general, the carbon supports used in the present invention are wellknown in the art. Activated, non-graphitized carbon supports arepreferred. These supports are characterized by high adsorptive capacityfor gases, vapors, and colloidal solids and relatively high specificsurface areas. The support suitably may be a carbon, char, or charcoalproduced by means known in the art, for example, by destructivedistillation of wood, peat, lignite, coal, nut shells, bones, vegetable,or other natural or synthetic carbonaceous matter, but preferably is“activated” to develop adsorptive power. Activation usually is achievedby heating to high temperatures (from about 800° to about 900° C.) withsteam or with carbon dioxide which brings about a porous particlestructure and increased specific surface area. In some cases,hygroscopic substances, such as zinc chloride and/or phosphoric acid orsodium sulfate, are added before the destructive distillation oractivation, to increase adsorptive capacity. Preferably, the carboncontent of the carbon support ranges from about 10% for bone charcoal toabout 98% for some wood chars and nearly 100% for activated carbonsderived from organic polymers. The non-carbonaceous matter incommercially available activated carbon materials normally will varydepending on such factors as precursor origin, processing, andactivation method. Many commercially available carbon supports containsmall amounts of metals. Carbon supports having the fewestoxygen-containing functional groups at their surfaces are mostpreferred.

The form of the carbon support is not critical. In one embodiment ofthis invention, the support is a monolithic support. Suitable monolithicsupports may have a wide variety of shapes. Such a support may be, forexample, in the form of a screen or honeycomb. Such a support may also,for example, be in the form of a reactor impeller.

In a particularly preferred embodiment, the support is in the form ofparticulates. Because particulate supports are especially preferred,most of the following discussion focuses on embodiments which use aparticulate support. It should be recognized, however, that thisinvention is not limited to the use of particulate supports.

Suitable particulate supports may have a wide variety of shapes. Forexample, such supports may be in the form of granules. Even morepreferably, the support is in the form of a powder. These particulatesupports may be used in a reactor system as free particles, or,alternatively, may be bound to a structure in the reactor system, suchas a screen or an impeller.

Typically, a support which is in particulate form comprises a broad sizedistribution of particles. For powders, preferably at least about 95% ofthe particles are from about 2 to about 300 μm in their largestdimension, more preferably at least about 98% of the particles are fromabout 2 to about 200 μm in their largest dimension, and most preferablyabout 99% of the particles are from about 2 to about 150 μm in theirlargest dimension with about 95% of the particles being from about 3 toabout 100 μm in their largest dimension. Particles being greater thanabout 200 μm in their largest dimension tend to fracture into super-fineparticles (i.e., less than 2 μm in their largest dimension), which aredifficult to recover.

The specific surface area of the carbon support, measured by the BET(Brunauer-Emmett-Teller) method using N₂, is preferably from about 10 toabout 3,000 m²/g (surface area of carbon support per gram of carbonsupport), more preferably from about 500 to about 2,100 m²/g, and stillmore preferably from about 750 to about 2,100 m²/g. In some embodiments,the most preferred specific surface area is from about 750 to about1,750 m²/g.

The pore volume of the support may vary widely. Using the measurementmethod described in Example 1, the pore volume preferably is from about0.1 to about 2.5 ml/g (pore volume per gram of catalyst), morepreferably from about 0.2 to about 2.0 ml/g, and most preferably fromabout 0.4 to about 1.7 ml/g. Catalysts comprising supports with porevolumes greater than about 2.5 ml/g tend to fracture easily. On theother hand, catalysts comprising supports having pore volumes less than0.1 ml/g tend to have small surface areas and therefore low activity.

Carbon supports for use in the present invention are commerciallyavailable from a number of sources. The following is a listing of someof the activated carbons which may be used with this invention: DarcoG-60 Spec and Darco X (ICI-America, Wilmington, Del.); Norit SG Extra,Norit EN4, Norit EXW, Norit A, Norit Ultra-C, Norit ACX, and Norit 4×14mesh (Amer. Norit Co., Inc., Jacksonville, Fla.); Gl-9615, VG-8408,VG-8590, NB-9377, XZ, NW, and JV (Barnebey-Cheney, Columbus, Ohio); BLPulv., PWA Pulv., Calgon C 450, and PCB Fines (Pittsburgh ActivatedCarbon, Div. of Calgon Corporation, Pittsburgh, Pa.); P-100 (No. Amer.Carbon, Inc., Columbus, Ohio); Nuchar CN, Nuchar C-1000 N, Nuchar C-190A, Nuchar C-115 A, and Nuchar SA-30 (Westvaco Corp., Carbon Department,Covington, Va.); Code 1551 (Baker and Adamson, Division of Allied Amer.Norit Co., Inc., Jacksonville, Fla.); Grade 235, Grade 337, Grade 517,and Grade 256 (Witco Chemical Corp., Activated Carbon Div., New York,N.Y.); and Columbia SXAC (Union Carbide New York, N.Y.).

The catalyst of this invention preferably has one or more noble metal(s)at its surface. Preferably, the noble metal(s) is selected from thegroup consisting of platinum (Pt), palladium (Pd), ruthenium (Ru),rhodium (Rh), iridium (Ir), silver (Ag), osmium (Os), and gold (Au). Ingeneral, platinum and palladium are more preferred, and platinum is mostpreferred. Because platinum is presently the most preferred noble metal,the following discussion will be directed primarily to embodiments usingplatinum. It should be understood, however, that the same discussion isgenerally applicable to the other noble metals and combinations thereof.It also should be understood that the term “noble metal” as used hereinmeans the noble metal in its elemental state as well as the noble metalin any of its various oxidation states.

The concentration of the noble metal deposited at the surface of thecarbon support may vary within wide limits. Preferably, it is in therange of from about 0.5 to about 20 wt. % ([mass of noble metal÷totalmass of catalyst]×100%), more preferably from about 2.5 to about 10 wt.%, and most preferably from about 3 to about 7.5 wt. %. Ifconcentrations less than 0.5 wt. % are used during the PMIDA oxidationreaction, there tends to be less formaldehyde oxidized, and therefore agreater amount of NMG produced, thereby reducing theN-(phosphonomethyl)glycine yield. On the other hand, at concentrationsgreater than about 20 wt. %, layers and clumps of noble metal tend toform. Thus, there are fewer surface noble metal atoms per total amountof noble metal used. This tends to reduce the activity of the catalystand is an uneconomical use of the costly noble metal.

The dispersion of the noble metal at the surface of the carbon supportpreferably is such that the concentration of surface noble metal atomsis from about 10 to about 400 μmole/g (μmole of surface noble metalatoms per gram of catalyst), more preferably, from about 10 to about 150μmole/g, and most preferably from about 15 to about 100 μmole/g. Thismay be determined, for example, by measuring chemisorption of H₂ or COusing a Micromeritics ASAP 2010C (Micromeritics, Norcross, Ga.) or anAltamira AMI100 (Zeton Altamira, Pittsburgh, Pa.).

Preferably, the noble metal is at the surface of the carbon support inthe form of metal particles. At least about 90% (number density) of thenoble metal particles at the surface of the carbon support arepreferably from about 0.5 to about 35 nm in their largest dimension,more preferably from about 1 to about 20 nm in their largest dimension,and most preferably from about 1.5 to about 10 nm in their largestdimension. In a particularly preferred embodiment, at least about 80% ofthe noble metal particles at the surface of the carbon support are fromabout 1 to about 15 nm in their largest dimension, more preferably fromabout 1.5 to about 10 nm in their largest dimension, and most preferablyfrom about 1.5 to about 7 nm in their largest dimension. If the noblemetal particles are too small, there tends to be an increased amount ofleaching when the catalyst is used in an environment that tends tosolubilize noble metals, as is the case when oxidizing PMIDA to formN-(phosphonomethyl)glycine. On the other hand, as the particle sizeincreases, there tends to be fewer noble metal surface atoms per totalamount of noble metal used. As discussed above, this tends to reduce theactivity of the catalyst and is also an uneconomical use of the costlynoble metal.

In addition to the noble metal, at least one promoter may be at thesurface of the carbon support. As defined herein, a “promoter” is ametal that tends to increase catalyst selectivity, activity, and/orstability. A promoter additionally may reduce noble metal leaching.Although the promoter usually is deposited onto the surface of thecarbon support in a promoter deposition step, the carbon support itselfmay also (or alternatively) naturally contain a promoter. A promoterwhich is deposited or exists naturally on the catalyst surface beforethe carbon support surface is finally reduced (see Section (B)(4) below)is referred to herein as a “catalyst-surface promoter.”

The catalyst-surface promoter may, for example, be an additional noblemetal(s) at the surface of the carbon support. For example, depending onthe application, ruthenium and palladium may act as catalyst-surfacepromoters on a catalyst comprising platinum deposited at a carbonsupport surface. The catalyst-surface promoter(s) alternatively may be,for example, a metal selected from the group consisting of tin (Sn),cadmium (Cd), magnesium (Mg), manganese (Mn), nickel (Ni), aluminum(Al), cobalt (Co), bismuth (Bi), lead (Pb), titanium (Ti), antimony(Sb), selenium (Se), iron (Fe), rhenium (Re), zinc (Zn), cerium (Ce),zirconium (Zr), tellurium (Te), and germanium (Ge). Preferably, thecatalyst-surface promoter is selected from the group consisting ofbismuth, iron, tin, titanium and tellurium. In a particularly preferredembodiment, the catalyst-surface promoter is tin. In anotherparticularly preferred embodiment, the catalyst-surface promoter isiron. In an additional preferred embodiment, the catalyst-surfacepromoter is titanium. In a further particularly preferred embodiment,the catalyst comprises both iron and tin at its surface. Use of iron,tin, or both generally (1) reduces noble metal leaching for a catalystused over several cycles, and (2) tends to increase and/or maintain theactivity of the catalyst when the catalyst is used to effect theoxidation of PMIDA. Catalysts comprising iron generally are mostpreferred because they tend to have the greatest activity and stabilitywith respect to formaldehyde and formic acid oxidation.

In a preferred embodiment, the catalyst-surface promoter is more easilyoxidized than the noble metal (in instances where the catalyst-surfacepromoter is a noble metal as well, the catalyst-surface promoter noblemetal preferably is more easily oxidized than the non-promoter noblemetal). A promoter is “more easily oxidized” if it has a lower firstionization potential than the noble metal. First ionization potentialsfor the elements are widely known in the art and may be found, forexample, in the CRC Handbook of Chemistry and Physics (CRC Press, Inc.,Boca Raton, Fla.).

The amount of catalyst-surface promoter at the surface of the carbonsupport (whether associated with the carbon surface itself, metal, or acombination thereof) may vary within wide limits depending on, forexample, the noble metal(s) and catalyst-surface promoter(s) used.Typically, the weight percentage of the catalyst-surface promoter is atleast about 0.05% ([mass of catalyst-surface promoter÷total mass of thecatalyst]×100%). The weight percent of the catalyst-surface promoterpreferably is from about 0.05 to about 10%, more preferably from about0.1 to about 10%, still more preferably from about 0.1 to about 2%, andmost preferably from about 0.2 to about 1.5%. When the catalyst-surfacepromoter is tin, the weight percent most preferably is from about 0.5 toabout 1.5%. Catalyst-surface promoter weight percentages less than 0.05%generally do not promote the activity of the catalyst over an extendedperiod of time. On the other hand, weight percents greater than about10% tend to decrease the activity of the catalyst.

The molar ratio of noble metal to catalyst-surface promoter (and, ininstances where the catalyst-surface promoter is a noble metal as well,the molar ratio of the non-promoter noble metal to the catalyst-surfacepromoter noble metal) may also vary widely, depending on, for example,the noble metal(s) and catalyst-surface promoter(s) used. Preferably,the ratio is from about 1000:1 to about 0.01:1; more preferably fromabout 150:1 to about 0.05:1; still more preferably from about 50:1 toabout 0.05:1; and most preferably from about 10:1 to about 0.05:1. Forexample, a catalyst comprising platinum and iron preferably has a molarratio of platinum to iron of about 3:1.

In a particularly preferred embodiment of this invention, the noblemetal (e.g., Pt) is alloyed with at least one catalyst-surface promoter(e.g., Sn, Fe, or both) to form alloyed metal particles (and, ininstances where the catalyst-surface promoter is a noble metal as well,the non-promoter noble metal preferably is alloyed with thecatalyst-surface promoter noble metal). A catalyst comprising a noblemetal alloyed with at least one catalyst-surface promoter tends to haveall the advantages discussed above with respect to catalysts comprisinga catalyst-surface promoter in general. Catalysts comprising a noblemetal alloyed with at least one catalyst-surface promoter also tend toexhibit greater resistance to catalyst-surface promoter leaching andfurther stability from cycle to cycle with respect to formaldehyde andformic acid oxidation. See, e.g., Example 17.

The term “alloy” encompasses any metal particle comprising a noble metaland at least one catalyst-surface promoter, irrespective of the precisemanner in which the noble metal and catalyst-surface promoter atoms aredisposed within the particle (although it is generally preferable tohave a portion of the noble metal atoms at the surface of the alloyedmetal particle). The alloy may be, for example, any of the following:

-   -   1. An intermetallic compound. An intermetallic compound is a        compound comprising a noble metal and a promoter (e.g., Pt₃Sn).    -   2. A substitutional alloy. A substitutional alloy has a single,        continuous phase, irrespective of the concentrations of the        noble metal and promoter atoms. Typically, a substitutional        alloy contains noble metal and promoter atoms which are similar        in size (e.g., platinum and silver; or platinum and palladium).        Substitutional alloys are also referred to as “monophasic        alloys.”    -   3. A multiphasic alloy. A multiphasic alloy is an alloy that        contains at least two discrete phases. Such an alloy may        contain, for example Pt₃Sn in one phase, and tin dissolved in        platinum in a separate phase.    -   4. A segregated alloy. A segregated alloy is a metal particle        wherein the particle stoichiometry varies with distance from the        surface of the metal particle.    -   5. An interstitial alloy. An interstitial alloy is a metal        particle wherein the noble metal and promoter atoms are combined        with non-metal atoms, such as boron, carbon, silicon, nitrogen,        phosphorus, etc.

Preferably, at least about 80% (number density) of the alloyed metalparticles are from about 0.5 to about 35 nm in their largest dimension,more preferably from about 1 to about 20 nm in their largest dimension,still more preferably from about 1 to about 15 nm in their largestdimension, and most preferably from about 1.5 to about 7 nm in theirlargest dimension.

The alloyed metal particles need not have a uniform composition; thecompositions may vary from particle to particle, or even within theparticles themselves. In addition, the catalyst may further compriseparticles consisting of the noble metal alone or the catalyst-surfacepromoter alone. Nevertheless, it is preferred that the composition ofmetal particles be substantially uniform from particle to particle andwithin each particle, and that the number of noble metal atoms inintimate contact with catalyst-surface promoter atoms be maximized. Itis also preferred, although not essential, that the majority of noblemetal atoms be alloyed with a catalyst-surface promoter, and morepreferred that substantially all of the noble metal atoms be alloyedwith a catalyst-surface promoter. It is further preferred, although notessential, that the alloyed metal particles be uniformly distributed atthe surface of the carbon support.

Regardless of whether the catalyst-surface promoter is alloyed to thenoble metal, it is presently believed that the catalyst-surface promotertends to become oxidized if the catalyst is exposed to an oxidant over aperiod of time. For example, an elemental tin catalyst-surface promotertends to oxidize to form Sn(II)O, and Sn(II)O tends to oxidize to formSn(IV)O₂. This oxidation may occur, for example, if the catalyst isexposed to air for more than about 1 hour. Although suchcatalyst-surface promoter oxidation has not been observed to have asignificant detrimental effect on noble metal leaching, noble metalsintering, catalyst activity, or catalyst stability, it does makeanalyzing the concentration of detrimental oxygen-containing functionalgroups at the surface of the carbon support more difficult. For example,as discussed above, the concentration of detrimental oxygen-containingfunctional groups (i.e., oxygen-containing functional groups that reducenoble metal resistance to leaching and sintering, and reduce theactivity of the catalyst) may be determined by measuring (using, forexample, TGA-MS) the amount of CO that desorbs from the catalyst underhigh temperatures in an inert atmosphere. However, it is presentlybelieved that when an oxidized catalyst-surface promoter is present atthe surface, the oxygen atoms from the oxidized catalyst-surfacepromoter tend to react with carbon atoms of the support at hightemperatures in an inert atmosphere to produce CO, thereby creating theillusion of more detrimental oxygen-containing functional groups at thesurface of the support than actually exist. Such oxygen atoms of anoxidized catalyst-surface promoter also can interfere with obtaining areliable prediction of noble metal leaching, noble metal sintering, andcatalyst activity from the simple measurement (via, for example, x-rayphotoelectron spectroscopy) of oxygen atoms at the catalyst surface.

Thus, when the catalyst comprises at least one catalyst-surface promoterwhich has been exposed to an oxidant and thereby has been oxidized(e.g., when the catalyst has been exposed to air for more than about 1hour), it is preferred that the catalyst-surface promoter first besubstantially reduced (thereby removing the oxygen atoms of the oxidizedcatalyst-surface promoter from the surface of the catalyst) beforeattempting to measure the amount of detrimental oxygen-containingfunctional groups at the surface of the carbon support. This reductionpreferably is achieved by heating the catalyst to a temperature of about500° C. for about 1 hour in an atmosphere consisting essentially of H₂.The measurement of detrimental oxygen-containing functional groups atthe surface preferably is performed (a) after this reduction, and (b)before the surface is exposed to an oxidant following the reduction.Most preferably, the measurement is taken immediately after thereduction.

The preferred concentration of metal particles at the surface of thecarbon support depends, for example, on the size of the metal particles,the specific surface area of the carbon support, and the concentrationof noble metal on the catalyst. It is presently believed that, ingeneral, the preferred concentration of metal particles is roughly fromabout 3 to about 1,500 particles/μm² (i.e., number of metal particlesper μm² of surface of carbon support), particularly where: (a) at leastabout 80% (number density) of the metal particles are from about 1.5 toabout 7 nm in their largest dimension, (b) the carbon support has aspecific surface area of from about 750 to about 2100 m²/g (i.e., m² ofsurface of carbon support per gram of carbon support), and (c) theconcentration of noble metal at the carbon support surface is from about1 to about 10 wt. % ([mass of noble metal÷total mass of catalyst]×100%).In more preferred embodiments, narrower ranges of metal particleconcentrations and noble metal concentrations are desired. In one suchembodiment, the concentration of metal particles is from about 15 toabout 800 particles/μm², and the concentration of noble metal at thecarbon support surface is from about 2 to about 10 wt. %. In an evenmore preferred embodiment, the concentration of metal particles is fromabout 15 to about 600 particles/μm², and the concentration of noblemetal at the carbon support surface is from about 2 to about 7.5 wt. %.In the most preferred embodiment, the concentration of the metalparticles is from about 15 to about 400 particles/μm², and theconcentration of noble metal at the carbon support surface is about 5wt. %. The concentration of metal particles at the surface of the carbonsupport may be measured using methods known in the art.

B. Process for the Preparation of the Oxidation Catalyst

1. Deoxygenation of the Carbon Support

The surface of the carbon support preferably is deoxygenated before thenoble metal is deposited onto it. Preferably, the surface isdeoxygenated using a high-temperature deoxygenation treatment. Such atreatment may be a single-step or a multi-step scheme which, in eithercase, results in an overall chemical reduction of oxygen-containingfunctional groups at the surface of the carbon support.

In a two-step high-temperature deoxygenation treatment, the carbonsupport preferably is first treated with a gaseous or liquid phaseoxidizing agent to convert oxygen-containing functionalities inrelatively lower oxidation states (e.g., ketones, aldehydes, andalcohols) into functionalities in relatively higher oxidation states(e.g., carboxylic acids), which are easier to cleave from the surface ofthe catalyst at high temperatures. Representative liquid phase oxidizingagents include nitric acid, H₂O₂, chromic acid, and hypochlorite, withconcentrated nitric acid comprising from about 10 to about 80 grams ofHNO₃ per 100 grams of aqueous solution being preferred. Representativegaseous oxidants include molecular oxygen, ozone, nitrogen dioxide, andnitric acid vapors. Nitric acid vapors are the preferred oxidizingagent. With a liquid oxidant, temperatures in the range of from about60° to about 90° C. are appropriate, but with gaseous oxidants, it isoften advantageous to use temperatures of from about 50° to about 500°C. or even greater. The time during which the carbon is treated with theoxidant can vary widely from about 5 minutes to about 10 hours.Preferably, the reaction time is from about 30 minutes to about 6 hours.Experimental results indicate that carbon load, temperature, oxidantconcentration, etc. in the first treatment step are not narrowlycritical to achieving the desired oxidation of the carbon material andthus may be governed by convenience over a wide range. The highestpossible carbon load is preferred for economic reasons.

In the second step, the oxidized carbon support is pyrolyzed (i.e.,heated) at a temperature preferably in the range of from about 500° toabout 1500° C., and more preferably from about 600° to about 1,200° C.,in a nitrogen, argon, helium, or other non-oxidizing environment (i.e.,an environment consisting essentially of no oxygen) to drive off theoxygen-containing functional groups from the carbon surface. Attemperatures greater than about 500° C., an environment may be usedwhich comprises a small amount of ammonia (or any other chemical entitywhich will generate NH₃ during pyrolysis), steam, or carbon dioxide, allof which may aid in the pyrolysis. As the temperature of the carbonsupport is cooled to temperatures less than about 500° C., however, thepresence of oxygen-containing gases such as steam or carbon dioxide maylead to the re-formation of surface oxides and thus, is preferablyavoided. Accordingly, the pyrolysis is preferably conducted in anon-oxidizing atmosphere (e.g., nitrogen, argon, or helium). In oneembodiment, the non-oxidizing atmosphere comprises ammonia, which tendsto produce a more active catalyst in a shorter time as compared topyrolysis in the other atmospheres. The pyrolysis may be achieved, forexample, using a rotary kiln, a fluidized bed reactor, or a conventionalfurnace.

The carbon support generally is pyrolyzed for a period of from about 5minutes to about 60 hours, preferably from about 10 minutes to about 6hours. Shorter times are preferred because prolonged exposure of thecarbon at elevated temperatures tends to reduce the activity of thecatalyst. Without being bound to any particular theory, it is presentlybelieved that prolonged heating at pyrolytic temperatures favors theformation of graphite, which is a less preferred form of a carbonsupport because it normally has less surface area. As discussed above, amore active catalyst typically may be produced in a shorter time byusing an atmosphere which comprises ammonia.

In a preferred embodiment of this invention, high-temperaturedeoxygenation is carried out in one step. This one-step treatment mayconsist of merely performing the pyrolysis step of the two-stephigh-temperature deoxygenation treatment discussed above. Morepreferably, however, the single-step treatment consists of pyrolyzingthe carbon support as described above while simultaneously passing a gasstream comprising N₂, NH₃ (or any other chemical entity which willgenerate NH₃ during pyrolysis), and steam over the carbon. Although itis not a critical feature of this invention, the flow rate of the gasstream preferably is fast enough to achieve adequate contact between thefresh gas reactants and the carbon surface, yet slow enough to preventexcess carbon weight loss and material waste. A non-reactive gas may beused as a diluent to prevent severe weight loss of the carbon.

2. Deposition of the Noble Metal(s)

Methods used to deposit the noble metal onto the surface of the carbonsupport are generally known in the art, and include liquid phase methodssuch as reaction deposition techniques (e.g., deposition via reductionof noble metal compounds, and deposition via hydrolysis of noble metalcompounds), ion exchange techniques, excess solution impregnation, andincipient wetness impregnation; vapor phase methods such as physicaldeposition and chemical deposition; precipitation; electrochemicaldeposition; and electroless deposition. See generally, Cameron, D. S.,Cooper, S. J., Dodgson, I. L., Harrison, B., and Jenkins, J. W. “Carbonsas Supports for Precious Metal Catalysts,” Catalysis Today, 7, 113-137(1990). Catalysts comprising noble metals at the surface of a carbonsupport also are commercially available, e.g., Aldrich Catalog No.20,593-1, 5% platinum on activated carbon (Aldrich Chemical Co., Inc.,Milwaukee, Wis.); Aldrich Catalog No. 20,568-0, 5% palladium onactivated carbon.

Preferably, the noble metal is deposited via a reactive depositiontechnique comprising contacting the carbon support with a solutioncomprising a salt of the noble metal, and then hydrolyzing the salt. Anexample of a suitable platinum salt which is relatively inexpensive ishexachloroplatinic acid (H₂PtCl₆). The use of this salt to depositplatinum onto a carbon support via hydrolytic deposition is illustratedin Example 3.

In one embodiment of this invention, the noble metal is deposited ontothe surface of the carbon support using a solution comprising a salt ofa noble metal in one of its more reduced oxidation states. For example,instead of using a salt of Pt(IV) (e.g., H₂PtCl₆), a salt of Pt(II) isused. In another embodiment, platinum in its elemental state (e.g.,colloidal platinum) is used. Using these more reduced metal precursorsleads to less oxidation of the carbon support and, therefore, lessoxygen-containing functional groups being formed at the surface of thesupport while the noble metal is being deposited onto the surface. Oneexample of a Pt(II) salt is K₂PtCl₄. Another potentially useful Pt(II)salt is diamminedinitrito platinum(II). Example 11 shows that using thissalt to deposit the noble metal produces a catalyst which is moreresistant to leaching than a catalyst prepared using H₂PtCl₆ as themetal precursor. Without being bound by any particular theory, it isbelieved that this is due to the fact that diamminedinitritoplatinum(II) generates ammonia in-situ during reduction which furtherpromotes removal of the oxygen-containing functional groups at thesurface of the carbon support. This benefit, however, should be weighedagainst a possible explosion danger associated with the use ofdiamminedinitrito platinum(II).

3. Deposition of a Catalyst-Surface Promoter(s)

A catalyst-surface promoter(s) may be deposited onto the surface of thecarbon support before, simultaneously with, or after deposition of thenoble metal onto the surface. Methods used to deposit a promoter ontothe surface of the carbon support are generally known in the art, andinclude the same methods used to deposit a noble metal discussed above.In one embodiment, a salt solution comprising a promoter is used todeposit the catalyst-surface promoter. A suitable salt that may be usedto deposit bismuth is Bi(NO₃)₃.5H₂O, a suitable salt that may be used todeposit iron is FeCl₃.6H2O, and a suitable salt that may be used todeposit tin is SnCl₂.2H₂O. It should be recognized that more than onecatalyst-surface promoter may be deposited onto the surface of thecarbon support. Examples 13, 14, 15, and 17 demonstrate depositing apromoter onto a carbon surface with a salt solution comprising apromoter. Example 18 demonstrates depositing more than one promoter(i.e., iron and Sn) onto a carbon surface using salt solutionscomprising the promoters.

As noted above, a catalyst comprising a noble metal alloyed with atleast one catalyst-surface promoter is particularly preferred. There area variety of possible preparative techniques known in the art which maybe used to form a multi-metallic alloy at support surfaces. See, e.g.,V. Ponec & G. C. Bond, Catalysis by Metals and Alloys, “Studies inSurface Science and Catalysis,” Vol. 95 (B. Delmon. & J. T. Yates,advisory eds., Elsevier Science B.V., Amsterdam, Netherlands).

In one of the more preferred embodiments, reactive deposition is used toform metal particles containing a noble metal alloyed with acatalyst-surface promoter. Reactive deposition may comprise, forexample, reductive deposition wherein a surface of a carbon support iscontacted with a solution comprising: (a) a reducing agent; and (b) (i)a compound comprising the noble metal and a compound comprising thepromoter, or (ii) a compound comprising both the noble metal and thepromoter. A wide range of reducing agents may be used, such as sodiumborohydride, formaldehyde, formic acid, sodium formate, hydrazinehydrochloride, hydroxylamine, and hypophosphorous acid. Compoundscomprising a noble metal and/or a promoter include, for example:

-   -   1. Halide compounds. These include, for example, H₂PtCl₆,        K₂PtCl₄, Pt₂Br₆ ²⁻, K₂PdCl₄, AuCl₄ ¹⁻, RuCl₃, RhCl₃.3H2O,        K₂RuCl₆, FeCl₃.6H₂O, (SnCl₃)¹⁻, SnCl₄, ReCl₆, FeCl₂, and TiCl₄.    -   2. Oxide and oxy chloride compounds. These include, for example,        RuO₄ ²⁻ and M₂SnO₄.    -   3. Nitrate compounds. These include, for example, Fe(NO₃)₃.    -   4. Amine complexes. These include, for example, [Pt(NH₃)₄]Cl₂,        [Pd(NH₃)₄]Cl₂, Pt(NH₃)₂Cl₂, Pt(NH₃)₄]PtCl₄, Pd(NH₂CH₂CH₂NH₂)Cl₂,        Pt(NH₂CH₂CH₂NH₂)₂Cl₂, and [Ru(NH₃)₅Cl]Cl₂.    -   5. Phosphine complexes. These include, for example,        Pt(P(CH₃)₃)₂Cl₂; IrClCO(P(C₆H₅)₃)₂; PtClH(PR₃)₂, wherein each R        is independently a hydrocarbyl, such as methyl, ethyl, propyl,        phenyl, etc    -   6. Organometallic complexes. These include, for example,        Pt₂(C₃H₆)₂Cl₄; Pd₂(C₂H₄)₂Cl₄; Pt(CH₃COO)₂, Pd(CH₃COO)₂;        K[Sn(HCOO)₃]; Fe(CO)₅; Fe₃(CO)₁₂; Fe₄(CO)₁₆; Sn₃(CH₃)₄; and        Ti(OR)₄, wherein each R is independently a hydrocarbyl, such as        methyl, ethyl, propyl, phenyl, etc.    -   7. Noble metal/promoter complexes. These include, for example,        Pt₃(SnCl₃)₂(C₈H₁₂)₃ and [Pt(SnCl₃)₅]³⁻.

In a particularly preferred embodiment, hydrolysis reactions are used todeposit a noble metal alloyed with a catalyst-surface promoter. In thisinstance, ligands containing the noble metal and promoter are formed,and then hydrolyzed to form well-mixed, metal oxide and metal hydroxideclusters at the surface of the carbon support. The ligands may beformed, for example, by contacting the surface of the support with asolution comprising (a) a compound comprising the noble metal and acompound comprising the promoter, or (b) a compound comprising both thenoble metal and the promoter. Suitable compounds comprising a noblemetal and/or a promoter are listed above with respect to reductivedeposition. Hydrolysis of the ligands may be achieved, for example, byheating (e.g., at a temperature of at least about 60° C.) the mixture.Example 17 further demonstrates the use of hydrolysis reactions todeposit a noble metal (i.e., platinum) alloyed with a catalyst-surfacepromoter (i.e., iron).

In addition to the above-described reactive deposition techniques, thereare many other techniques which may be used to form the alloy. Theseinclude, for example:

-   -   1. Forming the alloy by introducing metal compounds (which may        be simple or complex, and may be covalent or ionic) to the        surface of the support via impregnation, adsorption from a        solution, and/or ion exchange.    -   2. Forming the alloy by vacuum co-deposition of metal vapors        containing the noble metal and promoter onto the surface.    -   3. Forming the alloy by depositing one or more metals onto a        pre-deposited metal belonging to Group 8, 9, or 10 of the        Periodic Table of the Elements (i.e., Fe, Co, Ni, Ru, Rh, Pd,        Os, Ir, and Pt) via, for example, electrolytic or electroless        plating.    -   4. Forming the alloy by: (a) depositing metal complexes        containing metals in the zero valence state (e.g., carbonyl,        pi-allyl, or cyclopentadienyl complexes of the noble metal and        of the promoter) at the surface of the carbon support; and (b)        removing the ligands by, for example, heating or reduction to        form the alloy particles at the surface.    -   5. Forming the alloy by contacting a solution containing a metal        compound (e.g., a metal chloride or a metal alkyl compound) with        a pre-deposited metal hydride containing a metal belonging to        Group 8, 9, or 10 of the Periodic Table of the Elements.    -   6. Forming the alloy by co-depositing, either simultaneously or        sequentially, metal complexes (either pre-formed or formed in        situ) containing the noble metal(s) and promoter(s) at the        surface of the carbon support.    -   7. Forming the alloy by pre-forming alloy particles as colloids        or aerosols, and then depositing the pre-formed alloy particles        at the surface of the carbon support. To illustrate, colloidal        particles containing platinum and iron may be easily formed by        boiling a dilute solution of H₂PtCl₆ and SnCl₂.2H₂O with a        sodium citrate solution. Protecting agents (e.g., carbohydrates,        polymers, lipophilic quaternary nitrogen salts) may be used to        effectively control metal alloy particle growth. This technique,        therefore, is often useful to form a narrow distribution of        alloy particle sizes.

It should be recognized that the above-discussed techniques for formingan alloy are simply illustrative, and not exhaustive. Using theteachings of this specification and the general knowledge of the art,one of ordinary skill in the art may routinely determine which of thenumerous alloy preparation techniques known in the art are suitable to aparticular use.

Regardless of the technique used to form the alloy, after the metalshave been deposited at the surface of the carbon support, it is oftenpreferable to dry the support using, for example, a sub-atmospheric,non-oxidizing environment (preferably, N₂, a noble gas, or both). Use ofa drying step is particularly preferred where the surface of the supportis to be subsequently reduced by heating the surface (and even morepreferred where the heating is to be conducted in a non-oxidizingenvironment). Preferably, the support is dried to reduce the moisturecontent of the support to less than about 5% by weight.

It should be recognized that reducing the surface of the carbon supportafter deposition of the noble metal(s) and catalyst-surface promoter(s)typically increases the extent of noble metal alloyed with acatalyst-surface promoter. Such reduction also often tends to increasethe number of particles falling within the preferred size range.

4. Reduction of the Carbon Support Surface

After the carbon support has been impregnated with the noble metal(s)(and catalyst-surface promoter(s), if any), the surface of the catalystpreferably is reduced. The surface of the catalyst suitably may bereduced, for example, by heating the surface at a temperature of atleast about 400° C. It is especially preferable to conduct this heatingin a non-oxidizing environment (e.g., nitrogen, argon, or helium). It isalso more preferred for the temperature to be greater than about 500° C.Still more preferably, the temperature is from about 550° to about1,200° C., and most preferably from about 550° to about 900° C.Temperatures less than 400° C. tend to be unsatisfactory for removingthe oxygen-containing functional groups from the surface of the carbonsupport. On the other hand, temperatures greater than 1,200° C. tend toreduce the activity of the catalyst. Temperatures of from about 400° toabout 500° C. preferably are used only if the surface of the carbonsupport has a carbon atom to oxygen atom ratio of at least about 20:1before the noble metal is deposited onto the surface.

In a particularly preferred embodiment, the surface of the catalyst isreduced by a process comprising exposing the surface to a reducingenvironment. For example, before the heating, the catalyst sample may bepre-treated with a liquid-phase reducing agent, such as formaldehyde orformic acid. Even more preferably, the heating is conducted in thepresence of a gas-phase reducing agent (the method of heating thecatalyst in the presence of a gas-phase reducing agent will sometimes bereferred to as “high-temperature gas-phase reduction”). Variousgas-phase reducing agents may be used during the heating, including butnot limited to H₂, ammonia, and carbon monoxide. Hydrogen gas is mostpreferred because the small molecular size of hydrogen allows betterpenetration into the deepest pores of the carbon support. Preferably,the remainder of the gas consists essentially of a non-oxidizing gas,such as nitrogen, argon, or helium. The gas may comprise any finiteconcentration of H₂, although H₂ concentrations of less than about 1.0%are disadvantageous because of the time they tend to require to reducethe surface of the support. Preferably, the gas comprises from about 5to about 50 volume % H₂, and most preferably from about 5 to about 25volume % H₂.

The preferred amount of time that the catalyst surface is heated dependson the rate of mass transfer of the reducing agent to the catalystsurface. When the reducing agent is a non-oxidizing gas comprising fromabout 10 to about 20 volume % H₂, the surface preferably is heated for atime of from about 15 minutes to about 24 hours at a temperature of fromabout 550° to about 900° C. with a space velocity within the range offrom about 1 to about 5,000 hour⁻¹. More preferably, the space velocityis from about 10 to about 2,500 hour⁻¹, and even more preferably fromabout 50 to about 750 hour⁻¹. In the most preferred embodiment, theheat-treatment is conducted at the above preferred temperatures andspace velocities for a time of from about 1 to about 10 hours. Heatingthe surface at space velocities of less than about 1 hour⁻¹ isdisadvantageous because the oxygen-containing functional groups at thesurface of the carbon support may not be sufficiently destroyed. On theother hand, heating the surface at space velocities greater than about5,000 hour⁻¹ is not economical.

Pre-existing oxygen-containing functional groups at the surface of thecarbon support generally are not necessary, or even desired, to obtainadequate noble metal dispersion and retention. Without being bound byany particular theory, it is believed that this heating step enhancesthe platinum-carbon interaction on the catalyst by removingoxygen-containing functional groups at the surface of the carbonsupport, including those formed by depositing the noble metal onto thesurface. It is believed that these oxygen-containing functional groupsare unstable anchor sites for the noble metal because they tend tointerfere with the potentially stronger H interactions between the noblemetal and the carbon support. Heating alone will decompose and therebyremove many of the oxygen-containing functional groups at the surface ofthe carbon support. However, by heating the surface in the presence of areducing agent (e.g., H₂), more oxygen-containing functional groups areable to be eliminated.

If the carbon atom to oxygen atom ratio at the surface of the carbonsupport is less than about 20:1 before the noble metal is deposited ontothe surface of the support, the surface preferably is reduced using theabove-described high-temperature gas-phase reduction treatment at atemperature greater than about 500° C., although the surface mayoptionally be treated with other reducing environments in addition tohigh-temperature gas-phase reduction. On the other hand, if the surfaceof the carbon support has a carbon atom to oxygen atom ratio which is atleast about 20:1 before the noble metal is deposited onto the surface,various alternative reducing environments may be used instead ofhigh-temperature gas-phase reduction.

The surface of the catalyst may be reduced, at least in part, bytreating it with an amine, such as urea, a solution comprising ammoniumions (e.g., ammonium formate or ammonium oxalate), or ammonia gas, withammonia gas or a solution comprising ammonium ions being most preferred.This amine treatment preferably is used in addition to other reductiontreatments, and most preferably is used before high-temperaturegas-phase reduction. In one such embodiment, the noble metal isdeposited onto the surface by treating it with a noble metal precursorsolution comprising ammonium ions. Alternatively, after the noble metalis deposited onto the surface of the support, the support may be washedwith a solution comprising ammonium ions or placed into contact with agas comprising ammonia. Most preferably, the catalyst surface is washedwith diluted aqueous ammonia after depositing the noble metal. In thisinstance, the catalyst is added to pure water and stirred for a fewhours to wet the surface of the catalyst. Next, while continuing to stirthe catalyst slurry, a solution comprising ammonium ions is added to thecatalyst slurry in an amount sufficient to produce a pH of greater thanabout 7, more preferably from about 8 to about 12, and most preferablyfrom about 9.5 to about 11.0. Because the temperature and pressure arenot critical, this step preferably is performed at room temperature andatmospheric pressure. Example 10 further demonstrates this reductiontreatment.

Sodium borohydride (NaBH₄) also may be used to reduce the surface of thecatalyst. As with the amine treatment, this treatment preferably is usedin addition to other reduction treatments, and most preferably is usedbefore high-temperature gas-phase reduction. Preferably, afterdepositing the noble metal onto the surface of the support, the supportis washed with a solution of NaBH₄ in the presence of NaOH at a pH offrom about 8 to about 14 for a period of time of from about 15 to about180 minutes. The amount of NaBH₄ used preferably is sufficient to reduceall the noble metal. Because the temperature and pressure are notcritical, this step preferably is performed at room temperature andatmospheric pressure. Example 12 further demonstrates this reductiontreatment.

It should be recognized that any of the above treatments which may beused to reduce the surface of the catalyst also may be used todeoxygenate the surface of the carbon support before the noble metal isdeposited onto the surface.

C. Use of the Oxidation Catalyst

The above-described catalyst may be used for liquid phase oxidationreactions. Examples of such reactions include the oxidation of alcoholsand polyols to form aldehydes, ketones, and acids (e.g., the oxidationof 2-propanol to form acetone, and the oxidation of glycerol to formglyceraldehyde, dihydroxyacetone, or glyceric acid); the oxidation ofaldehydes to form acids (e.g., the oxidation of formaldehyde to formformic acid, and the oxidation of furfural to form 2-furan carboxylicacid); the oxidation of tertiary amines to form secondary amines (e.g.,the oxidation of nitrilotriacetic acid (“NTA”) to form iminodiaceticacid (“IDA”)); the oxidation of secondary amines to form primary amines(e.g., the oxidation of IDA to form glycine); and the oxidation ofvarious acids (e.g., formic acid or acetic acid) to form carbon dioxideand water.

The above-described catalyst is especially useful in liquid phaseoxidation reactions at pH levels less than 7, and in particular, at pHlevels less than 3. It also is especially useful in the presence ofsolvents, reactants, intermediates, or products which solubilize noblemetals. One such reaction is the oxidation of PMIDA, a salt of PMIDA, oran ester of PMIDA to form N-(phosphonomethyl)glycine, a salt ofN-(phosphonomethyl)glycine, or an ester of N-(phosphonomethyl)glycine inan environment having pH levels in the range of from about 1 to about 2.The description below will disclose with particularity the use of theabove-described catalyst to effect the oxidative cleavage of PMIDA, asalt of PMIDA, or an ester of PMIDA to form N-(phosphonomethyl)glycine,a salt of N-(phosphonomethyl)glycine, or an ester ofN-(phosphonomethyl)glycine. It should be recognized, however, that theprinciples disclosed below are generally applicable to other liquidphase oxidative reactions, especially those at pH levels less than 7 andthose involving solvents, reactants, intermediates, or products whichsolubilize noble metals.

To begin the PMIDA oxidation reaction, it is preferable to charge thereactor with the PMIDA substrate (i.e., PMIDA, a salt of PMIDA, or anester of PMIDA), catalyst, and a solvent in the presence of oxygen. Thesolvent is most preferably water, although other solvents (e.g., glacialacetic acid) are suitable as well.

The reaction may be carried out in a wide variety of batch, semi-batch,and continuous reactor systems. The configuration of the reactor is notcritical. Suitable conventional reactor configurations include, forexample, stirred tank reactors, fixed bed reactors, trickle bedreactors, fluidized bed reactors, bubble flow reactors, plug flowreactors, and parallel flow reactors, with stirred tank reactors oftenbeing most preferred.

FIG. 1 shows one example of a batch-type embodiment that may be used inaccordance with this invention. In this particular embodiment, theoxidation substrate (e.g., PMIDA, a salt of PMIDA, and/or an ester ofPMIDA) is introduced into a stirred-tank reactor 3, along with a solvent(most preferably water) and oxygen (e.g., pure oxygen or air). Thecatalyst is maintained in a catalyst holding tank 1 (also called a“catalyst recycle tank”), and then moved to the stirred-tank reactor 3to catalyze the oxidation reaction. After essentially all the oxidationsubstrate has been consumed by the oxidation reaction, the reactionmixture 4 (including the reaction product and the catalyst) istransferred to a filter holding tank 5, and then to a filter 7 wheresubstantially all the catalyst is separated from substantially all thereaction product to form a catalyst stream 9 (containing the catalyst,and, typically, a residual amount of the reaction product) and a productstream 8 containing substantially all the reaction product. The catalyststream 9 is directed to the catalyst holding tank 1, while the reactionproduct stream 8 is carried forward for further processing forcommercial use. It should be recognized, however, that a portion of theproduct stream 8 may alternatively, for example, be recycled back to thestirred-tank reactor 3 to supply formaldehyde and/or formic acid to actas a sacrificial reducing agent during a subsequent batch oxidationreaction, as discussed below. For example, the reaction product stream 8can be passed through an evaporator (not shown) where essentially allthe N-(phosphonomethyl)glycine product is precipitated and a separatestream (not shown) is formed containing evaporated formaldehyde, formicacid, and water which is recycled (in whole or in part) back to thestirred-tank reactor 3. Because water is also being recycled, thisrecycle scheme has the additional benefit of conserving water andreducing waste volume.

When the oxidation reaction is conducted in a continuous reactor system,the residence time in the reaction zone can vary widely depending on thespecific catalyst and conditions employed. Typically, the residence timecan vary over the range of from about 3 to about 120 minutes.Preferably, the residence time is from about 5 to about 90 minutes, andmore preferably from about 5 to about 60 minutes. When the oxidationreaction is conducted in a batch reactor, the reaction time typicallyvaries over the range of from about 15 to about 120 minutes. Preferably,the reaction time is from about 20 to about 90 minutes, and morepreferably from about 30 to about 60 minutes.

In a broad sense, the oxidation reaction may be practiced in accordancewith the present invention at a wide range of temperatures, and atpressures ranging from sub-atmospheric to super-atmospheric. Use of mildconditions (e.g., room temperature and atmospheric pressure) haveobvious commercial advantages in that less expensive equipment may beused. However, operating at higher temperatures and super-atmosphericpressures, while increasing plant costs (equipment and operating costs),tends to improve phase transfer between the liquid and gas phase (e.g.,the oxygen source) and increase the PMIDA oxidation reaction rate.

Preferably, the PMIDA reaction is conducted at a temperature of fromabout 20° to about 180° C., more preferably from about 50° to about 140°C., and most preferably from about 80° about 110° C. At temperaturesgreater than about 180° C., the raw materials tend to slowly decompose.

The pressure used during the PMIDA oxidation generally depends on thetemperature used. Preferably, the pressure is sufficient to prevent thereaction mixture from boiling. If an oxygen-containing gas is used asthe oxygen source, the pressure also preferably is adequate to cause theoxygen to dissolve into the reaction mixture at a rate sufficient suchthat the PMIDA oxidation is not limited due to an inadequate oxygensupply. The pressure preferably is at least equal to atmosphericpressure. More preferably, the pressure is from about 30 to about 500psig (about 206 to about 3447 kPa), and most preferably from about 30 toabout 130 psig (about 206 to about 896 kPa).

The catalyst concentration preferably is from about 0.1 to about 10 wt.% ([mass of catalyst÷total reaction mass]×100%). More preferably, thecatalyst concentration is from about 0.2 to about 5 wt. %, even morepreferably from about 0.3 to about 1.5 wt. %, still even more preferablyfrom about 0.5 to about 1.0 wt. %, and most preferably about 0.75 wt. %.Concentrations greater than about 10 wt. % are difficult to filter. Onthe other hand, concentrations less than about 0.1 wt. % tend to produceunacceptably low reaction rates.

The concentration of the PMIDA substrate in the feed stream is notcritical. Use of a saturated solution of PMIDA substrate in water ispreferred, although for ease of operation, the process is also operableat lesser or greater PMIDA substrate concentrations in the feed stream.If the catalyst is present in the reaction mixture in a finely dividedform, it is preferred to use a concentration of reactants such that allreactants and the N-(phosphonomethyl)glycine product remain in solutionso that the catalyst can be recovered for re-use, for example, byfiltration. On the other hand, greater concentrations tend to increasereactor throughput. Alternatively, if the catalyst is present as astationary phase through which the reaction medium and oxygen source arepassed, it may be possible to use greater concentrations of reactantssuch that a portion of the N-(phosphonomethyl)glycine productprecipitates.

It should be recognized that, relative to many commonly-practicedcommercial processes, this invention allows for greater temperatures andPMIDA substrate concentrations to be used to prepareN-(phosphonomethyl)glycine while minimizing by-product formation. In thecommonly practiced commercial processes using a carbon-only catalyst, itis economically beneficial to minimize the formation of the NMGby-product formed by the reaction of N-(phosphonomethyl)glycine with theformaldehyde by-product. With those processes and catalysts,temperatures of from about 60° to about 90° C. and PMIDA substrateconcentrations below about 9.0 wt. % ([mass of PMIDA substrate÷totalreaction mass]×100%) typically are used to achieve cost effective yieldsand to minimize the generation of waste. At such temperatures, themaximum N-(phosphonomethyl)glycine solubility typically is less thanabout 6.5%. However, with the oxidation catalyst and reaction process ofthe present invention, the loss of noble metal from the catalyst andcatalyst deactivation are minimized and the formaldehyde is moreeffectively oxidized, thereby allowing for reaction temperatures as highas 180° C. or greater with PMIDA solutions and slurries of the PMIDAsubstrate. The use of greater temperatures and reactor concentrationspermits reactor throughput to be increased, reduces the amount of waterthat must be removed before isolation of the solidN-(phosphonomethyl)glycine, and reduces the cost of manufacturingN-(phosphonomethyl)glycine. This invention thus provides economicbenefits over many commonly-practiced commercial processes.

Normally, a PMIDA substrate concentration of up to about 50 wt. % ([massof PMIDA substrate÷total reaction mass]×100%) may be used (especially ata reaction temperature of from about 20° to about 180° C.). Preferably,a PMIDA substrate concentration of up to about 25 wt. % is used(particularly at a reaction temperature of from about 60° to about 150°C.). More preferably, a PMIDA substrate concentration of from about 12to about 18 wt. % is used (particularly at a reaction temperature offrom about 100° to about 130° C.). PMIDA substrate concentrations below12 wt. % may be used, but their use is less economical because lessN-(phosphonomethyl)glycine product is produced in each reactor cycle andmore water must be removed and energy used per unit ofN-(phosphonomethyl)glycine product produced. Lower temperatures (i.e.,temperatures less than 100° C.) often tend to be less advantageousbecause the solubility of the PMIDA substrate andN-(phosphonomethyl)glycine product are both reduced at suchtemperatures.

The oxygen source for the PMIDA oxidation reaction may be anyoxygen-containing gas or a liquid comprising dissolved oxygen.Preferably, the oxygen source is an oxygen-containing gas. As usedherein, an “oxygen-containing gas” is any gaseous mixture comprisingmolecular oxygen which optionally may comprise one or more diluentswhich are non-reactive with the oxygen or with the reactant or productunder the reaction conditions. Examples of such gases are air, puremolecular oxygen, or molecular oxygen diluted with helium, argon,nitrogen, or other non-oxidizing gases. For economic reasons, the oxygensource most preferably is air or pure molecular oxygen.

The oxygen may be introduced by any conventional means into the reactionmedium in a manner which maintains the dissolved oxygen concentration inthe reaction mixture at the desired level. If an oxygen-containing gasis used, it preferably is introduced into the reaction medium in amanner which maximizes the contact of the gas with the reactionsolution. Such contact may be obtained, for example, by dispersing thegas through a diffuser such as a porous frit or by stirring, shaking, orother methods known to those skilled in the art.

The oxygen feed rate preferably is such that the PMIDA oxidationreaction rate is not limited by oxygen supply. If the dissolved oxygenconcentration is too high, however, the catalyst surface tends to becomedetrimentally oxidized, which, in turn, tends to lead to more leachingand decreased formaldehyde activity (which, in turn, leads to more NMGbeing produced).

Generally, it is preferred to use an oxygen feed rate such that at leastabout 40% of the oxygen is utilized. More preferably, the oxygen feedrate is such that at least about 60% of the oxygen is utilized. Evenmore preferably, the oxygen feed rate is such that at least about 80% ofthe oxygen is utilized. Most preferably, the rate is such that at leastabout 90% of the oxygen is utilized. As used herein, the percentage ofoxygen utilized equals: (the total oxygen consumption rate÷oxygen feedrate)×100%. The term “total oxygen consumption rate” means the sum of:(i) the oxygen consumption rate (“R_(i)”) of the oxidation reaction ofthe PMIDA substrate to form the N-(phosphonomethyl)glycine product andformaldehyde, (ii) the oxygen consumption rate (“R_(ii)”) of theoxidation reaction of formaldehyde to form formic acid, and (iii) theoxygen consumption rate (“R_(iii)”) of the oxidation reaction of formicacid to form carbon dioxide and water.

In one embodiment of this invention, oxygen is fed into the reactor asdescribed above until the bulk of PMIDA substrate has been oxidized, andthen a reduced oxygen feed rate is used (by, for example, using areduced feed rate of the oxygen source, or using an oxygen source havinga reduced O₂ concentration (e.g., air) at a volumetric feed rate whichpreferably is no greater than the volumetric feed rate of the initialoxygen source). This reduced feed rate preferably is used after about75% of the PMIDA substrate has been consumed. More preferably, thereduced feed rate is used after about 80% of the PMIDA substrate hasbeen consumed. The reduced oxygen feed rate preferably is maintained fora time of from about 2 to about 40 min., more preferably from about 5 toabout 30 min., and most preferably from about 5 to about 20 min. Whilethe oxygen is being fed at the reduced rate, the temperature preferablyis maintained at the same temperature or at a temperature less than thetemperature at which the reaction was conducted before the air purge.Likewise, the pressure is maintained at the same pressure or at apressure less than the pressure at which the reaction was conductedbefore the air purge. Use of a reduced oxygen feed rate near the end ofthe PMIDA reaction tends to reduce the amount of residual formaldehydepresent in the reaction solution without producing detrimental amountsof AMPA by oxidizing the N-(phosphonomethyl)glycine product.

Reduced losses of noble metal may be observed with this invention if asacrificial reducing agent is maintained or introduced into the reactionsolution. Suitable reducing agents include formaldehyde, formic acid,and acetaldehyde. Most preferably, formic acid, formaldehyde, ormixtures thereof (which, for example, may often advantageously beobtained from waste streams of this process) are used. If small amountsof formic acid, formaldehyde, or a combination thereof are added to thereaction solution, the catalyst will often preferentially effect theoxidation of the formic acid or formaldehyde before it effects theoxidation of the PMIDA substrate, and subsequently will be more activein effecting the oxidation of formic acid and formaldehyde during thePMIDA oxidation. Preferably from about 0.01 to about 5.0 wt. % ([mass offormic acid, formaldehyde, or a combination thereof÷total reactionmass]×100%) of sacrificial reducing agent is added, more preferably fromabout 0.01 to about 3.0 wt. % of sacrificial reducing agent is added,and most preferably from about 0.01 to about 1.0 wt. % of sacrificialreducing agent is added.

In one embodiment, following the PMIDA oxidation, the catalystpreferably is separated by filtration. The N-(phosphonomethyl)glycineproduct may then be isolated by precipitation, for example, byevaporation of a portion of the water and cooling. Unreactedformaldehyde and formic acid are recovered from theN-(phosphonomethyl)glycine product mixture in an evaporator to form anoverhead vapor stream containing evaporated formaldehyde and formic acidwhich is condensed and recycled (in whole or in part) back into thereaction mixture for use in subsequent cycles. In this instance, therecycle stream also may be used to solubilize the PMIDA substrate in thesubsequent cycles.

Typically, the concentration of N-(phosphonomethyl)glycine in theproduct mixture may be as great as 40% by weight, or greater.Preferably, the N-(phosphonomethyl)glycine concentration is from about 5to about 40%, more preferably from about 8 to about 30%, and still morepreferably from about 9 to about 15%. Concentrations of formaldehyde inthe product mixture are typically less than about 0.5% by weight, morepreferably less than about 0.3%, and still more preferably less thanabout 0.15%.

It should be recognized that the catalyst of this invention has theability to be reused over several cycles (i.e., it may be used tocatalyze multiple batches of substrate), depending on how oxidized itssurface becomes with use. Even after the catalyst becomes heavilyoxidized, it may be reused by being reactivated. To reactivate acatalyst having a heavily oxidized surface, the surface preferably isfirst washed to remove the organics from the surface. It then preferablyis reduced in the same manner that a catalyst is reduced after the noblemetal is deposited onto the surface of the support, as described above.

D. Use of a Supplemental Promoter

In many conventional processes, when it is desirable for a catalyst tocontain a promoter, the promoter is pre-deposited onto the catalystsurface by, for example, the promoter deposition techniques describedabove (this deposition step is often performed by the manufacturer ofthe catalyst). This promoter deposition step, however, tends to addcosts to the catalyst preparation process. To avoid these additionalcosts, it has been found that the benefits of a promoter (e.g.,increased selectivity, activity, and/or catalyst stability) may beobtained by merely mixing a promoter (i.e., a “supplemental promoter”)directly with a carbon-supported, noble-metal-containing catalyst(particularly with the reduced catalysts described above). This mixingmay, for example, be conducted directly in a reaction mixture where anoxidation reaction being catalyzed by the catalyst is taking place.Alternatively, for example, this mixing may take place separately fromthe oxidation reaction, such as in a catalyst holding tank.

In accordance with the present invention, it has been discovered thatcertain metals and/or metal compounds function as supplemental promotersin an oxidation reaction catalyzed by a carbon-supported,noble-metal-containing catalyst. More particularly, it has been foundthat such supplemental promoters are effective in enhancing thecapability of noble metal on carbon catalysts for catalyzing theoxidation of such substrates such as formaldehyde, formic acid, andN-(phosphonomethyl)iminodiacetic acid. The supplemental promoters havebeen found especially useful in the oxidation ofN-(phosphonomethyl)iminodiacetic acid to N-(phosphonomethyl)glycine(glyphosate) wherein they are effective in enhancing catalysis of thedesired conversion to glyphosate, the oxidation of by-productformaldehyde to formic acid, and the oxidation of by-product formic acidto carbon dioxide. The supplemental promoters have been found usefulboth in the in situ oxidation of these by-products in theN-(phosphonomethyl)iminodiacetic acid oxidation reaction zone, and inthe oxidation of aqueous formaldehyde and formic acid fractions obtainedby distillation or evaporation from the glyphosate reaction mass.

Depending on the application, the supplemental promoter(s) may be, forexample, tin, cadmium, magnesium, manganese, ruthenium, nickel, copper,aluminum, cobalt, bismuth, lead, titanium, antimony, selenium, iron,rhenium, zinc, cerium, zirconium, tellurium, sodium, potassium,vanadium, gallium, Ta, Nb, rubidium, cesium, lanthanum, and/orgermanium. It is often more preferred for the supplemental promoter(s)to be bismuth, lead, germanium, tellurium, titanium, copper and/ornickel.

In an especially preferred embodiment, the supplemental promoter isbismuth. It has been found in accordance with this invention that thepresence of bismuth is especially effective in enhancing the selectivityof a carbon-supported, noble-metal-containing catalyst (particularly thereduced catalyst described above) when it is used to catalyze theoxidation of a PMIDA substrate (e.g., PMIDA or a salt thereof) to forman N-(phosphonomethyl)glycine product (e.g., N-(phosphonomethyl)glycineor a salt thereof). More specifically, it has been found that thepresence of bismuth causes an increase in the amount of formic acidbyproduct that is catalytically oxidized. In some instances(particularly where the catalyst comprises tin as a catalyst-surfacepromoter), the presence of bismuth also has been found to cause anincrease in the amount of formaldehyde byproduct that is catalyticallyoxidized. This increased destruction of one or both of these byproducts,in turn, causes less NMG byproduct to be formed (it is believed thatthis stems from the fact that the formation of each molecule of NMGbyproduct requires either (a) two formaldehyde molecules, or (b) aformic acid molecule and a formaldehyde molecule). Further, it has beenfound that in some instances (particularly where more than onesupplemental promoter is used) that the presence of bismuth may alsoreduce the amount of noble metal that leaches from the carbon support ofthe catalyst during the oxidation of a PMIDA substrate.

In another preferred embodiment of this invention, tellurium is used asa supplemental promoter. As in the above embodiment incorporatingbismuth as a supplemental promoter, it has been found in accordance withthis invention that the presence of tellurim is also effective inenhancing the selectivity of a carbon-supported, noble-metal-containingcatalyst (particularly the reduced catalyst described above) when it isused to catalyze the oxidation of a PMIDA substrate (e.g., PMIDA or asalt thereof) to form an N-(phosphonomethyl)glycine product (e.g.,N-(phosphonomethyl)glycine or a salt thereof). More particularly,applicants have further found that tellurium may increase the activityof the catalyst in the oxidation of PMIDA. Further, applicants havefound that noble metal leaching from the carbon support of the catalystmay be reduced during the oxidation of a PMIDA substrate by the presenceof tellurium in the reaction medium (particularly when bismuth is alsopresent).

In a most preferred embodiment, two supplemental both bismuth andtellurium are used as supplemental promoters.

The mixing of the supplemental promoter and catalyst preferably isconducted in a liquid medium. As noted above, this mixing may, forexample, be conducted directly in a reaction medium where an oxidationreaction being catalyzed by the catalyst is taking place. Where,however, the oxidation reaction is carried out under pressure, thereaction vessel is normally sealed and it is consequently often morepreferred to mix the catalyst with the supplemental promoter separatelyfrom the reaction vessel, such as in a catalyst holding or recycle tank.

Typically, the supplemental promoter is introduced into the mixingliquid in the form of an inorganic or organic compound containing thesupplemental promoter. The promoter-containing compound may be solubleor insoluble in the liquid, but most typically is at least partiallysoluble. The functional group attached to the supplemental promoter atomis generally not critical (although it preferably is an agronomicallyacceptable functional group). Typically, for example, suitable compoundsinclude oxides, hydroxides, salts of inorganic hydracids, salts ofinorganic oxy-acids, salts of aliphatic or aromatic organic acids, andphenates.

Suitable bismuth-containing compounds, for example, include inorganic ororganic compounds wherein the bismuth atom(s) is at an oxidation levelgreater than 0 (e.g., 2, 3, 4 or 5), most preferably 3. Examples of suchsuitable bismuth compounds include:

-   -   1. Bismuth oxides. These include, for example, BiO, Bi₂O₃,        Bi₂O₄, Bi₂O₅, and the like.    -   2. Bismuth hydroxides. These include, for example, Bi(OH)₃ and        the like.    -   3. Bismuth salts of inorganic hydracids. These include, for        example, bismuth chloride (e.g., BiCl₃), bismuth bromide (e.g.,        BiBr₃), bismuth iodide (e.g., BiI₃), bismuth telluride (e.g.,        Bi₂Te₃), and the like. Bismuth halides are typically less        preferred because they tend to be corrosive to the process        equipment.    -   4. Bismuth salts of inorganic oxy-acids. These include, for        example, bismuth sulphite (e.g., Bi₂(SO₃)₃.Bi₂O₃.5H₂O), bismuth        sulphate (e.g., Bi₂(SO₄)₃), bismuthyl sulfate (e.g., (BiO)HSO₄),        bismuthyl nitrite (e.g., (BiO)NO₂.0.5H₂O), bismuth nitrate        (e.g., Bi(NO₃)₃.5H₂O, also known as “bismuth nitrate        pentahydrate”), bismuthyl nitrate (e.g., (BiO)NO₃, also known as        “bismuth subnitrate,” “bismuth nitrate oxide,” and “bismuth        oxynitrate”), double nitrate of bismuth and magnesium (e.g.,        2Bi(NO₃)₃.3Mg(NO₃)₂.24H₂O), bismuth phosphite (e.g.,        Bi₂(PO₃H)₃.3H₂O), bismuth phosphate (e.g., BiPO₄), bismuth        pyrophosphate (e.g., Bi₄(P₂O₇)₃), bismuthyl carbonate (e.g.,        (BiO)₂CO₃, also known as “bismuth subcarbonate”), bismuth        perchlorate (e.g., Bi(ClO₄)₃.5H₂O), bismuth antimonate (e.g.,        BiSbO₄), bismuth arsenate (e.g., Bi(AsO₄)₃), bismuth selenite        (e.g., Bi₂(SeO₂)₃), bismuth titanate (e.g., Bi₂O₃.2TiO₂), and        the like. These salts also include bismuth salts of oxy-acids        derived from transition metals, including, for example, bismuth        vanadate (e.g., BiVO₄), bismuth niobate (e.g., BiNbO₄), bismuth        tantalate (BiTaO₄), bismuth chromate (Bi₂(CrO₄), bismuthyl        dichromate (e.g., (BiO)₂Cr₂O₇), bismuthyl chromate (e.g.,        H(BiO)CrO₄), double chromate of bismuthyl and potassium (e.g.,        K(BiO)CrO₄), bismuth molybdate (e.g., Bi₂(MoO₄)₃), double        molybdate of bismuth and sodium (e.g., NaBi(MoO₄)₂), bismuth        tungstate (e.g., Bi₂(WO₄)₃), bismuth permanganate (e.g.,        Bi₂O₂(OH)MnO₄), bismuth zirconate (e.g., 2Bi₂O₃.3ZrO₂), and the        like.    -   5. Bismuth salts of aliphatic or aromatic organic acids. These        include, for example, bismuth acetate (e.g., Bi(C₂H₃O₂)₃),        bismuthyl propionate (e.g., (BiO)C₃H₅O₂), bismuth benzoate        (e.g., C₆H₅CO₂Bi(OH)₂), bismuthyl salicylate (e.g.,        C₆H₄CO₂(BiO)(OH)), bismuth oxalate (e.g., (C₂O₄)₃Bi₂), bismuth        tartrate (e.g., Bi₂(C₄H₄O₆)₃.6H₂O), bismuth lactate (e.g.,        (C₆H₉O₅)OBi.7H₂O), bismuth citrate (e.g., C₆H₅O₇Bi), and the        like.    -   6. Bismuth phenates. These include, for example, bismuth gallate        (e.g., C₇H₇O₇Bi), bismuth pyrogallate (e.g.,        C₆H₃(OH)₂(OBi)(OH)), and the like.    -   7. Miscellaneous other organic and inorganic bismuth compounds.        These include, for example, bismuth phosphide (e.g., BiP),        bismuth arsenide (Bi₃As₄), sodium bismuthate (e.g., NaBiO₃),        bismuth-thiocyanic acid (e.g., H₂(Bi(BNS)₅).H₃(Bi(CNS)₆)),        sodium salt of bismuth-thiocyanic acid, potassium salt of        bismuth-thiocyanic acid, trimethylbismuthine (e.g., Bi(CH₃)₃),        triphenylbismuthine (e.g., Bi(C₆H₅)₃), bismuth oxychloride        (e.g., BiOCl), bismuth oxyiodide (e.g., BiOI), and the like.

In a preferred embodiment, the bismuth compound is a bismuth oxide,bismuth hydroxide, or bismuth salt of an inorganic oxy-acid. Morepreferably, the bismuth compound is bismuth nitrate (e.g.,Bi(NO₃)₃.5H₂O), bismuthyl carbonate (e.g., (BiO)₂CO₃), or bismuth oxide(e.g., Bi₂O₃), with bismuth (III) oxide (i.e., Bi₂O₃) being mostpreferred because it contains no counterion which can contaminate thefinal reaction product.

Suitable tellurium-containing compounds, for example, include inorganicor organic compounds wherein the tellurium atom(s) is at an oxidationlevel greater than 0 (e.g., 2, 3, 4, 5 or 6), most preferably 4.Examples of such suitable tellurium compounds include:

-   -   1. Tellurium oxides. These include, for example, TeO₂, Te₂O₃,        Te₂O₅, TeO₃, and the like.    -   2. Tellurium salts of inorganic hydracids. These include, for        example, tellurium tetrachloride (e.g., TeCl₄), tellurium        tetrabromide (e.g., TeBr₄), tellurium tetraiodide (e.g., TeI₄),        and the like.    -   3. Tellurium salts of inorganic oxy-acids. These include, for        example, tellurious acid (e.g., H₂TeO₃), telluric acid (e.g.,        H₂TeO₄ or Te(OH)₆), tellurium nitrate (e.g., Te₂O₄.HNO₃), and        the like.    -   4. Miscellaneous other organic and inorganic tellurium        compounds. These include, for example, dimethyl tellurium        dichloride, lead tellurium oxide, tellurium isopropoxide,        ammonium tellurate, tellurium thiourea, and the like.

In a preferred embodiment, the tellurium compound is a tellurium oxideor tellurium salt of an inorganic hydracid. More preferably, thetellurium compound is tellurium dioxide (e.g., TeO₂), tellurimtetrachloride (e.g., TeCl₄), or telluric acid (e.g., Te(OH)₆), withtellurium tetrachloride being most preferred.

The preferred amount of the supplemental promoter introduced into thereaction zone depends on, for example, the mass of the carbon-supported,noble-metal-containing catalyst (i.e., the total mass of the carbonsupport, noble metal, and any other component of the catalyst); mass ofthe total reaction feed mixture; and the concentration of the oxidationsubstrate.

In general, the ratio of the mass of the supplemental promoter to themass of the carbon-supported, noble-metal-containing catalyst charged tothe reactor is preferably at least about 1:15,000; more preferably atleast about 1:5,000; even more preferably at least about 1:2500; andmost preferably at least about 1:1000. Although it is feasible topractice the present invention without detriment to the oxidationreaction when ratios of the mass of supplemental promoter to the mass ofthe carbon-supported, noble-metal-containing catalyst are as great asabout 1:750, about 1:500, about 1:300, and even greater than about 1:50or 1:40, the preferred lower ratios described above have been found tobe effective for most applications, and particularly for the specificembodiments described in the present invention while reducing the amountof supplemental promoter consumed.

The ratio of the mass of the supplemental promoter to the total reactionmass charged to the reactor is preferably at least about 1:1,000,000;more preferably at least about 1:100,000; even more preferably at leastabout 1:40,000; and most preferably from about 1:40,000 to about1:15,000. Although ratios greater than 1:8,000 may normally be usedwithout detriment to the oxidation reaction, it is generally preferredfor the ratio to be less than 1:8,000 (particularly where bismuth is thesupplemental promoter).

The ratio of the mass of the supplemental promoter to the mass of theoxidation substrate (e.g., PMIDA or a salt thereof) charged to thereactor is preferably at least about 1:100,000; more preferably1:10,000; even more preferably at least about 1:4,000; and mostpreferably from about 1:4,000 to about 1:2,000. Although ratios greaterthan 1:1,000 may normally be used without detriment to the oxidationreaction, it is generally preferred for the ratio to be less than1:1,000 (particularly where bismuth is the supplemental promoter).

Where a particulate noble metal on carbon catalyst is used for thereaction, both the catalyst and the supplemental promoter may be chargedto a liquid reaction medium in which the reaction is conducted. Forexample, in the preparation of N-(phosphonomethyl)glycine (glyphosate),the catalyst and supplemental promoter may be charged to an aqueousreaction medium containing N-(phosphonomethyl)iminodiacetic acid(PMIDA), and oxygen then introduced to the reaction medium for catalyticoxidation of PMIDA to glyphosate. The supplemental promoter may becharged in a mass ratio to the catalyst charge of at least about1:15,000, preferably at least about 1:5000, more preferably at leastabout 1:2500, and most preferably at least about 1:1000. As oxidation ofPMIDA to glyphosate proceeds, formaldehyde and formic acid by-productsare generated. The catalyst is effective to catalyze not only theoxidation of PMIDA but also the further oxidation of formaldehyde toformic acid, and formic acid to carbon dioxide. The presence of thesupplemental promoter is effective to enhance the catalytic oxidation ofthese by-products, especially for the conversion of formic acid to CO₂.

Where the oxidation reactions are conducted in a stirred tank reactor inwhich catalyst is slurried in the reaction medium, the catalyst isseparated from the reaction mixture, preferably by filtration, andrecycled to the reactor for further oxidation of PMIDA and the aforesaidby-products. Such a stirred tank reactor system may be operated ineither a batch or continuous mode. Alternatively, a fixed or fluidcatalyst bed can be used. In a continuous process, PMIDA, formaldehydeand formic acid are all oxidized in a continuous reaction zone to whichan aqueous reaction medium comprising PMIDA is continuously orintermittently supplied and a reaction mixture comprising glyphosate iscontinuously or intermittently withdrawn, the supplemental promoterbeing continuously or intermittently introduced into the reaction zone.

It has been observed that addition of a discrete charge of supplementalpromoter to the first batch of series of successive batch reactioncycles is effective to enhance the activity of the catalyst foroxidation of formic acid and formaldehyde throughout the series ofreaction cycles, without further addition of supplemental promoter fromany external source. It has further been observed that the supplementalpromoter is present in the recycled catalyst, apparently having beendeposited thereon by adsorption to the noble metal and/or the carbonsupport. Only a fraction of the supplemental promoter added to the firstbatch of the series can be found on the catalyst after multiple cycles.However, when supplemental promoter is introduced into the first batchin the amounts described above, the fraction remaining on the catalystis apparently sufficient for promoting the oxidation of formaldehyde andformic acid throughout the series of batches in which the catalystrecycled from an earlier batch is substantially the sole source ofsupplemental promoter for the successive batch reaction cycles of theseries. It has been found that a single addition of supplementalpromoter in a mass ratio to the catalyst of approximately 1:2500 iseffective for promotion of by-product oxidation in series of 20 or more,typically 50 or more, more typically over 100, batch reaction cycles.Thereafter, a further discrete charge of supplemental promoteroptionally may be added to the reaction medium for a subsequent batchconstituting the first of another series of batch oxidation reactioncycles in which the recycle catalyst from an earlier batch of suchfurther series becomes substantially the sole source of promoter for thesuccessive batch reaction cycles of the further series of batchreactions.

Similarly, where supplemental promoter is added to the reaction mediumin a continuous stirred tank reactor, addition of supplemental promoterin a single discrete amount is effective to enhance the effectiveness ofthe catalyst for formaldehyde and formic acid oxidation throughoutmultiple reactor turnovers of a continuous reaction run. No furtheraddition of supplemental promoter is made until the start of a secondreaction run. For this purpose, a reaction run consists of the period ofoxidation of formaldehyde and formic acid from the time of any discreteaddition of supplemental promoter to the reaction zone until the time ofthe next succeeding addition of supplemental promoter to the reactionzone, and may typically consist of 50 or more, more typically over 100,turnovers of the working volume of the reactor.

As noted, only a fraction of the supplemental promoter added to thefirst batch of a cycle remains on the catalyst after multiple cycles ofa series of batch reaction runs, or after multiple turnovers of acontinuous reaction run. However, the supplemental promoter remainseffective to enhance the oxidation of a substrate comprisingformaldehyde, or especially formic acid, if the substrate is contactedwith the oxidizing agent in a reaction zone which comprises the liquidreaction medium and wherein the mass ratio of supplemental promoter tothe catalyst in such reaction zone is at least about 1:200,000,preferably at least about 1:70,000, more preferably at least about1:30,000, most preferably at least about 1:15,000. Inasmuch assubstantially the sole source of supplemental promoter for the reactormay be recycle catalyst, it is further preferred that the supplementalpromoter be present on or in the recycle catalyst in the same massratios, i.e., at least about 1:200,000, preferably at least about1:70,000, more preferably at least about 1:30,000, most preferably atleast about 1:15,000.

The supplemental promoter content of the reaction zone can also beexpressed as a mass ratio to the noble metal component of the catalyst.For example, for a 5% noble metal on carbon catalyst, the ratio ofsupplemental promoter to noble metal should be at least about 1:10,000,more preferably 1:3500, more preferably 1:1800, most preferably 1:700.These preferences generally prevail over the range of noble metalcontent of the noble metal on carbon catalyst, which is typically fromabout 0.5 to 20% noble metal. However, where the noble metal content isrelatively high, e.g., approaching 20%, the supplemental promoter may beeffective in relatively lower mass ratios to the noble metal component,even as low as 1:40,000.

Where the supplemental promoter is added in a discrete charge at thestart of a series of batch reaction cycles, or at the beginning of acontinuous reaction run as defined above, it is added in a mass ratio tothe noble metal component of the catalyst of at least about 1:750,preferably at least about 1:250, more preferably at least about 1:125,most preferably at least about 1:50. As indicated above, the preferredratio of supplemental promoter to noble metal may vary with the noblemetal content of the catalyst. Thus, e.g., when the noble metal contentof the catalyst approaches 20% by weight, the supplemental promoter maybe effective when added at a mass ratio to noble metal of 1:3000 orhigher, more preferably at least about 1:1000, 1:500 or 1:200.

Periodic discrete additions of supplemental promoter may be advantageousbecause excessive proportions of supplemental promoter, while maximizingthe effectiveness of the catalyst for the oxidation of formaldehyde andformic acid, may retard the oxidation of PMIDA. By adding supplementalpromoter only periodically, the proportions of supplemental promoterdeposited on the catalyst and present in the reaction zone may decayfairly rapidly to a residual quasi-steady state range wherein thesupplemental promoter remains effective to enhance catalytic activityfor the oxidation of formaldehyde or formic acid without significantlyretarding the rate or extent of oxidation of PMIDA. In fact, while themass ratio preferences stated above apply to the oxidation offormaldehyde and formic acid, the preferred ratio may fall in anintermediate optimum range for a reaction comprising the conversion ofPMIDA to glyphosate. Thus, the optimum supplemental promoter contentwithin the PMIDA oxidation reaction zone, and on the recycle catalystfor such reaction, may be lower than 1:15,000, for example, in a rangeof 1:65,000 to 1:25,000.

Deposit of supplemental promoter on the surface of a noble metal oncarbon catalyst in the reaction medium results in formation of a novelcatalyst complex comprising the catalyst and the promoter. The catalystcomponent of the catalyst complex may further comprise a surfacepromoter comprising a metal different from the supplemental promoter or,in some instances, comprising the same metal. The supplemental promoteris believed to be deposited by adsorption from the reaction medium, andremains desorbable from the catalyst surface into the catalyst medium.While an operative fraction of residual supplemental promoter resistsdesorption to remain adhered to the catalyst through multiple reactioncycles (or through an extended run of a continuous reaction system) asexplained hereinabove, the supplemental promoter is typically moredesorbable than the surface promoter which is applied in the catalystpreparation process.

As described above, the catalyst is prepared in the first instance bydepositing noble metal and optionally surface promoter onto a carbonsupport to form a catalyst precursor, then reducing the catalystprecursor to produce the reaction catalyst. The novel catalyst complexis formed by subsequent deposition of supplemental promoter on theoxidation catalyst, typically by adsorption to the carbon or noble metalsurface. Advantageously, the supplemental promoter is mixed with theoxidation catalyst in the reaction medium so that the promoter isdeposited from the reaction medium onto the catalyst surface. However,it will be understood that, in the alternative, the supplementalpromoter can be premixed with the oxidation catalyst in another liquidmedium to form the catalyst complex, after which the catalyst complexmay be introduced into the reaction medium for use in conducting theoxidation reaction.

It should be recognized that, depending on the desired effects, morethan one supplemental promoter may be used. In addition, eachsupplemental promoter may come from more than one source. Further, thecarbon-supported, noble-metal-containing catalyst may already contain anamount of metal on its surface which is the same metal as thesupplemental promoter, such as where (a) the catalyst is manufacturedwith a such a metal on its surface to act as a catalyst-surfacepromoter, or (b) the catalyst is a used catalyst which has beenrecovered from a previous reaction mixture where the metal was present(e.g., as a supplemental promoter).

In a particularly preferred embodiment, the carbon-supported,noble-metal-containing catalyst itself also comprises one or morecatalyst-surface promoters on its surface, as described above (seeSections A and B(3)). Where the catalyst is being used in the oxidationof a PMIDA compound and the supplemental promoter is bismuth, it isparticularly preferred for the catalyst to contain tin and/or iron (thepresence of tin tends to be particularly useful for increasing theoxidation of the formaldehyde byproduct in addition to increasing theoxidation of the formic acid byproduct).

In many instances, after a supplemental promoter and a carbon-supported,noble-metal-containing catalyst have been combined, at least a portionof the supplemental promoter deposits onto the surface of the carbonsupport and/or noble metal of the catalyst, and is consequently retainedby the catalyst. Because the catalyst retains the promoter, the catalystmay typically be recycled for use in catalyzing the oxidation ofsubsequent amounts of the oxidation substrate (e.g., the catalyst may beused to oxidize additional batches of the oxidation substrate, or may beused in a continuous oxidation process) while still retaining thebenefits of the supplemental promoter. And, as the effects of thesupplemental promoter decrease over time with use, replenishing amountsof fresh supplemental promoter may periodically be mixed with thecatalyst to revive the effects and/or achieve other desired results(e.g., decreased formic acid levels). Where, for example, the catalystis used in multiple batch reactions, such periodic replenishing may, forexample, be conducted after the catalyst has been used in at least about20 batch oxidation reactions (more preferably after it has been used inat least about 30 batch oxidation reactions, and most preferably afterit has been used in at least about 100 or more batch oxidationreactions). Where a catalyst is periodically replenished with freshsupplemental promoter, the mixing for replenishment may be conductedduring, or, more preferably, separately from the oxidation reactionbeing catalyzed by the catalyst.

In a particularly preferred embodiment, a supplemental promoter is mixedwith a used catalyst (i.e., a catalyst that has been used in one or moreprevious oxidation reactions). Typically, the activity and/or desiredselectivity of a catalyst decreases with use over several cycles. Thus,for example, the activity of a carbon-supported, noble-metal-containingcatalyst for oxidizing byproducts (e.g., formaldehyde and/or formicacid) of the PMIDA oxidation reaction often tends to decrease as thecatalyst is used, thereby causing less formic acid and/or formaldehydeto be destroyed, and, consequently, a greater amount of NMG to beproduced. Eventually, in fact, this activity will decrease to a levelwhere an unacceptable amount of formic acid and/or formaldehyde is notoxidized, consequently often causing an unacceptable amount of NMGcompounds to be produced (i.e., the selectivity of the catalyst formaking N-(phosphonomethyl)glycine compounds from PMIDA compounds willdecrease to an unacceptable level). Traditionally, when the catalystactivity for oxidizing the byproducts reaches such a point, the catalysthas been deemed unuseable, and, consequently, has either been recycled(i.e., reactivated) through a time-consuming and sometimes costlyprocess, or discarded altogether. It has been discovered in accordancewith this invention, however, that such a catalyst can be “revived”(i.e., the selectivity of the catalyst for making theN-(phosphonomethyl)glycine compound can be increased to an acceptablelevel) by mixing the catalyst with a supplemental promoter, particularlybismuth or tellurium. In other words, the supplemental promoter can beused to modify the catalyst performance and extend the life of thecatalyst.

It has been observed that a supplemental promoter (particularly bismuth)may cause a slight decrease in the oxidation rate of PMIDA. In such aninstance, the oxidation rate may typically be increased, at least inpart, by increasing the amount of oxygen fed into the reacting mixture,maintaining a relatively high oxygen flowrate for an extended periodduring the reaction, and/or increasing the pressure. Where, however, theoxygen flow is increased, it preferably is not increased to an extentwhich causes the catalyst surface to become detrimentally over-oxidized.Thus, the increased oxygen feed rate preferably is maintained at a levelsuch that at least about 40% (more preferably at least about 60%, evenmore preferably at least about 80%, and most preferably at least about90%) of the fed oxygen is utilized.

E. Oxidation of Unreacted Formic Acid or Formaldehyde

As described above in Sections IV.C. and IV.D., the catalysts andsupplemental promoters of the present invention are useful in a varietyof liquid phase oxidation reactions including the oxidation of aldehydesto form acids (e.g., the oxidation of formaldehyde to form formic acid)and the oxidation of various acids (e.g., formic acid or acetic acid) toform carbon dioxide and water. Thus, in another particularly preferredembodiment of the present invention, it has been found that thecatalysts and supplemental promoters disclosed herein may be employedfor the catalytic oxidation of unreacted formic acid and/or formaldehyderecovered from the N-(phosphonomethyl)glycine product mixture producedin a process for the oxidation of N-(phosphonomethyl) iminodiacetic acidas described above.

Considerable quantities of formaldehyde and/or formic acid may beunreacted or generated as a waste stream from the manufacture ofN-(phosphonomethyl)glycine by the oxidation ofN-(phosphonomethyl)iminodiacetic acid. Typically, excess formaldehydeand/or formic acid are recovered from the N-(phosphonomethyl)glycineproduct mixture in an evaporator to form an overhead vapor streamcomprising formaldehyde, formic acid and/or water. In one embodiment, asdescribed above, the evaporated formaldehyde and formic acid in thisoverhead vapor stream may be condensed and recycled (in whole or inpart) back into the PMIDA reaction mixture for use in subsequent cyclesor to solubilize the PMIDA substrate. However, in other cases, it may benecessary or preferred to further treat the condensed formaldehyde orformic acid stream so as to comply with environmental regulations fordisposal or to further reduce the costs of obtaining process water. Forexample, one method for treating an aqueous stream of formaldehyde orformic acid is disclosed in U.S. Pat. No. 5,606,107, which is herebyincorporated by reference.

Referring now to FIG. 2, one embodiment for the oxidation of formic acidand/or formaldehyde produced as a byproduct from the production ofN-(phosphonomethyl)glycine by the oxidation of N-(phosphonomethyl)iminodiacetic acid is illustrated. In this embodiment, for example,reaction product stream 8 from FIG. 1 is passed through an evaporator 10where essentially all the N-(phosphonomethyl)glycine product 11 isprecipitated and a overhead vapor stream 15, which contains evaporatedformaldehyde, formic acid, and water is formed. The concentration offormaldehyde and/or formic acid in vapor stream 15 leaving theevaporator 10 may each be as high as about 7500 ppm, with typicalaverage concentrations of formaldehyde of about 6000 ppm and typicalaverage concentrations of formic acid of about 4000 ppm.

Vapor stream 15 is then condensed and the condensate is passed to anevaporator overhead recovery unit comprising an oxidation reactor 21wherein formic acid and/or formaldehyde are oxidized with oxygen in thepresence of a catalyst comprising a noble metal on a particulate carbonsupport. The oxidation reaction may be carried out in a wide variety ofreactor systems including any conventional batch, semi-batch, orcontinuous reactor system, with a continuous reactor system beingpreferred. The configuration of the reactor is not critical. Suitableconventional reactor configurations include, for example, stirred tankreactors, fixed bed reactors, trickle bed reactors, fluidized bedreactors, bubble flow reactors, plug flow reactors, and parallel flowreactors, with continuous stirred tank reactors being preferred.Accordingly, it has been found that a single-stage continuous stirredtank reactor is especially effective and such a single-stage continuousreactor system is most preferred.

The oxidation reaction mixture is preferably circulated over amicrofiltration unit 25 to separate a purified water stream 27 from thecatalyst slurry 29. The purified water stream 27 may be discharged orpreferably recycled back to the process for makingN-(phosphonomethyl)glycine by the oxidation ofN-(phosphonomethyl)iminodiacetic acid. The catalyst slurry 29 ispreferably recycled for subsequent use in the oxidation reactor 21.Suitable microfiltration units 25 may include any conventional filteringapparatus for separating a slurry from an aqueous stream, with apreferred microfiltration unit comprising a cross flow filter such as aHyPulse® filter commercially available from Mott Metallurgical Corp. ofFarmington, Conn.

In a typical embodiment utilizing a continuous oxidation reactor system,particulate catalyst is charged to the evaporator overhead recovery unitperiodically. After about four months the catalyst mass in the oxidationreactor as well as the microfilters need to be replaced due tocapacity-reduction caused by gradual microfilter plugging. Generally,this microfilter plugging is a result of an increase in dissolved oxygenin the reactor system. However, in accordance with the presentinvention, it has been found that the use of a supplemental promoter asdescribed above (particularly bismuth, tellurium, or a combination ofbismuth and tellurium) enhances the oxidation of formaldehyde and/orformic acid such that less catalyst has to be charged to the oxidationreactor over the standard four-month operation. Preferably, asupplemental promoter is sufficient to reduce the amount of catalystcharged to the oxidation reactor by about 20%, more preferably about 30%and most preferably about 40%. More importantly, it has been found thatthe use of a supplemental promoter as described above (particularlybismuth, tellurium, or a combination of bismuth and tellurium) enhancesthe activity and/or selectivity of the catalyst such that the life ofthe catalyst may be prolonged, thus reducing the amount of dissolvedoxygen in the reactor system such that effective life between changingof the microfiltration unit is also prolonged. More particularly, use ofa supplemental promoter in accordance with the present invention issufficient to prolong the effective catalyst life by at least about 10%,more preferably by at least about 15%, and most preferably by at leastabout 20%.

EXAMPLES

The following examples are simply intended to further illustrate andexplain the present invention. This invention, therefore, should not belimited to any of the details in these examples.

Example 1 Measuring Pore Volume of Carbon Support

A Micromeritics ASAP 2000 surface area and pore volume distributioninstrument was used to acquire the data. Total surface areadetermination involves exposing a known weight of a solid to somedefinite pressure of a non-specific adsorbate gas at a constanttemperature, e.g., at the temperature of liquid nitrogen, −196° C.During equilibration, gas molecules leave the bulk gas to adsorb ontothe surface which causes the average number of molecules in the bulk gasto decrease which, in turn, decreases the pressure. The relativepressure at equilibrium, p, as a fraction of the saturation vaporpressure, p_(o), of the gas is recorded. By combining this decrease inpressure with the volumes of the vessel and of the sample, the amount(i.e., the number of molecules) of gas adsorbed may be calculated byapplication of the ideal gas laws. These data are measured at relativepressures (p/p_(o)) of approximately 0.1 to 0.3 where the Brunauer,Emmett and Teller (BET) equation for multi-layer adsorption typicallyapplies. With the number of adsorbed gas molecules known, it is possibleto calculate the surface area using the “known” cross-sectional area ofthe adsorbate. For cases where only physical adsorption due to Van derWaals forces occurs (i.e., Type I Langmuir isotherms) the determinationof surface area from the observed changes in pressure is accomplishedusing the BET equation. Pore size and pore size distributions arecalculated by obtaining relative pressure data approaching p/p_(o)=1,i.e., in the regime where multi-layer adsorption and capillarycondensation occur. By applying the Kelvin equation and methodsdeveloped by Barrett, Joyner and Halenda (BJH), the pore volume and areamay be obtained.

Example 2 High-Temperature Deoxygenation of a Carbon Support

The high-temperature deoxygenation procedures described in the followingexamples may be used with any carbon support to produce a deoxygenatedcarbon support.

Single-Step High-Temperature Deoxygenation #1 Using NH₃/H₂O Gas

An activated carbon support (2.5 g) was placed into a 1.9 cm I.D.×40.6cm length quartz tube. The tube was connected to a gas stream resultingfrom sparging a 70 to 100 ml/min. N₂ stream through a 70° C., 10% NH₄OHaqueous solution. The quartz tube then was placed into a preheated 30.5cm tubular furnace and pyrolyzed at 930° C. for 60 min. and then cooledto room temperature under a dry N₂ atmosphere without contacting anyair.

Single-Step High-Temperature Deoxygenation #2 Using NH₃/H₂O Gas

An activated carbon support (3.55 g) was placed into a 1.9 cm I.D.×35.6cm long quartz tube. The tube was connected to streams of 50 ml/min. ofNH₃ gas and 89 ml/min. of steam and then placed into a preheated 30.5 cmtubular furnace and pyrolyzed at 930° C. for 30 minutes. The tubesubsequently was cooled to room temperature under a dry N₂ atmospherewithout any contact with air.

To show the advantages of deoxygenating the carbon support beforedispersing the noble metal onto the surface of the support, theperformances of the following two catalysts were compared: one having acarbon support, which was deoxygenated using the above treatment beforeplatinum was dispersed onto its surface; and one having an SA-30 carbonsupport (Westvaco Corp. Carbon, Department Covington, Va.) which wasused as received from Westvaco. Platinum was dispersed onto the surfacesof the carbon supports using the technique described in Example 3 below.The catalysts then were reduced. In one experiment, the catalysts werereduced using NaBH₄ (See Example 12 for protocol). In a secondexperiment, the catalysts were reduced by heating them in 20% H₂ and 80%argon for 8 hours at 640° C.

The reduced catalysts were used to catalyze the oxidation of PMIDA toN-(phosphonomethyl)glycine (i.e., “glyphosate”) using the reactionconditions set forth in Example 5. Table 1 shows the results. Use of thedeoxygenated carbon support resulted in smaller CO desorption values,less noble metal leaching, higher formaldehyde activity, and shorterreaction times. TABLE 1 Effect of Deoxygenating the Carbon Supportbefore Dispersing Noble Metal onto Its Surface CO desorption Pt in soln.Deoxygenation from carbon (μg/g glyph. CH₂O (mg/g Reaction treatmentsupport (mmole/g) Reduction prod.) glyph. prod.) time¹ (min.)Single-step 0.23 NaBH₄ 8.6 28.5 35.1 high-temperature Reduceddeoxygenation #2 (Ex. 12) SA-30, used as 1.99 same 54.3 43.1 62.7received Single-step 0.23 8 hrs at 4.8 15.6 29.8 high-temperature 640°C. in deoxygenation #2 20% H2, 80% Ar SA-30, used as 1.99 same 31 19.750.7 received¹When ≧98% of the PMIDA has been consumed.

Example 3 Depositing Platinum onto the Surface of a Carbon Support

Twenty grams of NUCHAR activated carbon SA-30 (Westvaco Corp. Carbon,Department Covington, Va.) was slurried in 2 L of water for 2 hours.Then, 2.81 grams of H₂PtCl₆ dissolved in about 900 ml of water was addeddropwise over a period of 3 to 4 hours. After the H₂PtCl₆ solution wascompletely added, the slurry was stirred for 90 more minutes. The pH ofthe slurry then was readjusted to 10.5 using NaOH, and stirred for 10 to14 more hours. The resulting slurry was filtered and washed with wateruntil the filtrate reached a constant conductivity. The wet cake wasdried at 125° C. under vacuum for 10 to 24 hours. This material produced5% platinum on carbon upon reduction.

It should be recognized that the above procedure may be used to depositplatinum onto the surface of other carbon supports as well.

Example 4 High-Temperature Hydrogen Reduction of a Carbon Support

Approximately 5.8 g of a dried, unreduced catalyst consisting of 5%platinum on a NUCHAR SA-30 carbon support (Westvaco Corp., CarbonDepartment, Covington, Va.) was dehydrated in-situ at 135° C. in argonfor one hour before being reduced at 640° C. with 20% H₂ in argon for 11hours. Upon cooling to room temperature under 20% H₂ in argon, thecatalyst was ready to use.

It should be recognized that the above procedure may be used to heatother carbon supports as well.

Example 5 Use of the Catalyst to Oxidize PMIDA toN-(Phosphonomethyl)glycine

This example demonstrates the use of high-temperature gas-phasereduction to improve catalyst performance.

An Aldrich catalyst consisting of 5% platinum on an activated carbonsupport (catalog No. 20,593-1, Aldrich Chemical Co., Inc., Milwaukee,Wis.) was heated at 640° C. for 4-6 hours in the presence of 20% H₂ and80% argon. Subsequently, it was used to catalyze the oxidation of PMIDAto Glyphosate. Its performance was compared to the performance of asample of the Aldrich catalyst which was used as received from Aldrich.

The PMIDA oxidation reaction was conducted in a 200 ml glass reactorusing 11.48 g of PMIDA, 0.5% catalyst (dry basis), a total reaction massof 140 g, a temperature of 90° C., a pressure of 50 psig, a stir rate of900 rpm, and an oxygen flow rate of 100 ml/min.

Table 2 shows the results. The high-temperature hydrogen-reducedcatalyst had less leaching, better formaldehyde activity, and producedless NMG. Also, reaction time was shortened by 30% when thehigh-temperature hydrogen-reduced catalyst was used. TABLE 2 PMIDAOxidation Results for 5% Pt on Activated Carbon (Aldrich Cat. No. 20,593-1) As Catalyst Received High-Temp., H₂ Reduced PMIDA (%) 0.46190.4430 N-(phosphonomethyl)glycine (%) 5.58 5.54 HCO₂H (mg/g glyph.prod.) 46.99 35.87 CH₂O (mg/g glyph. prod.) 32.96 14.60 NMG (mg/g glyph.prod.) 3.58 1.32 AMPA (ppm) 172.5 182.0 End Point (min.) 64.67 44.17 Ptin soln. (μg/g glyph. prod.) 32.26 10.50 % of Pt Lost 0.72 0.232

Example 6 Further Examples Showing Use of Catalyst to Oxidize PMIDA toN-(Phosphonomethyl)glycine

This example demonstrates using the high-temperature, gas-phasereduction treatment and ammonia washing to improve catalyst performance.

The performances of six catalysts in catalyzing the PMIDA oxidation werecompared. These catalysts were: (a) a catalyst consisting of 5% platinumon an activated carbon support (Catalog No. 33,015-9, Aldrich ChemicalCo., Inc., Milwaukee, Wis.); (b) the catalyst after being washed withammonia (ammonia washing was conducted using the same techniquedescribed in Example 10 except that the pH of the catalyst slurry wasadjusted to and maintained at 11.0 rather than 9.5); (c) the catalystafter being heated at 75° C. in 20% H₂ and 80% argon for 4-6 hours(GPR@75° C.); (d) the catalyst after being heated at 640° C. for 4-6hours in the presence of 20% H₂ and 80% argon (GPR@640° C.); and (e) twocatalysts after being washed with ammonia and then heated at 640° C. for4-6 hours in the presence of 20% H₂ and 80% argon. The PMIDA oxidationreaction conditions were the same as in Example 5.

Table 3 shows the results. The untreated catalyst showed relatively highleaching and poor formaldehyde activity. High-temperature gas-phasereduction at 640° C. in the presence of H₂ leads to the greatestdecrease in leaching and increase in formaldehyde activity. Heating thecatalyst at 75° C. in 20% H₂ at 75° C. decreased leaching to a lesserextent, but did not enhance the formaldehyde activity. TABLE 3 PMIDAOxidation Results for 5% Pt on Activated Carbon (Aldrich Cat. No. 33,015-9) As- NH₃ wash NH₃ wash + NH₃ wash + Catalyst received w/o GPR¹GPR@75° C. GPR@640° C. GPR@640° C. GPR@640° C. PMIDA (%) ND ND ND 0.0970.083 ND Glyphosate (%) 5.87 5.65 5.81 5.89 5.85 5.91 HCO₂H (mg/g glyph.43.46 43.65 38.97 42.14 46.91 52.12 prod.) CH₂O (mg/g glyph. 19.39 22.7319.85 13.78 15.70 17.61 prod.) NMG (mg/g glyph. 1.27 0.89 0.89 1.00 1.311.68 prod.) AMPA (ppm) 149.4 147.6 134.6 349.8 324.8 283.8 End Point(min.) 39.33 44.33 38 31.42 34.33 33.33 Pt in soln. (μg/g 42.59 40.7127.54 5.26 5.30 4.23 glyph. prod.) % of Pt Lost 1 0.92 0.64 0.12 0.120.1¹“GPR” means reduction in H₂2. “ND” means none detected.

In the next experiment, five catalysts were analyzed while catalyzingthe PMIDA oxidation. These catalysts were: (a) a catalyst consisting of5% platinum on NUCHAR SA-30 (Westvaco Corp., Carbon Department,Covington, Va.); (b) the catalyst after being treated with NaBH₄ (seeExample 12 for protocol); (c) the catalyst after being heated at 75° C.in 20% H₂ and 80% argon for 4-6 hours (GPR@75° C.); (d) the catalystafter being heated at 640° C. in 20% H₂ and 80% argon for 4-6 hours(GPR@640° C.); (e) the catalyst after being washed with ammonia (usingthe same technique described in Example 10) and then heated at 640° C.in 20% H₂ and 80% argon for 4-6 hours. The reaction conditions were thesame as those in Example 5.

Table 4 shows the results. The untreated catalyst showed relatively highplatinum leaching and low formaldehyde activity. The catalyst alsoshowed high leaching and low formaldehyde activity after being treatedwith NaBH₄, as did GPR@75° C. In contrast, GPR@640° C. showed a greaterformaldehyde activity and less leaching. TABLE 4 PMIDA Oxidation ResultsUsing 5% Pt on NUCHAR SA-30 NH₃ wash + Catalyst Unreduced NaBH₄ red.GPR@75° C. GPR@640° C. GPR@640° C. Glyphosate (%) 2.50 5.71 4.92 5.175.19 HCO₂H (mg/g glyph. 59.56 51.14 57.85 30.85 38.21 prod.) CH₂O (mg/gglyph. 115.28 43.13 48.52 19.67 20.79 prod.) NMG (mg/g glyph. 1.64 2.176.41 0.37 1.73 prod.) AMPA (ppm) 58.16 193.9 174.0 138.5 156.3 End point(min.) 62.67 62.67 70.67 50.67 59.33 Pt in soln. (μg/g 84.00 54.29 81.3030.95 19.27 glyph. prod.) % of Pt Lost 0.84 1.24 1.6 0.64 0.4

Example 7 Effect of C/O and O/Pt Ratios at the Surface of Catalyst

The carbon atom to oxygen atom ratio and the oxygen atom to platinumatom ratio at the surfaces of various fresh catalysts were analyzedusing a PHI Quantum 2000 ESCA Microprobe Spectrometer (PhysicalElectronics, Eden Prairie, Minn.). The surface analysis was performed byelectron spectroscopy for chemical analysis (“ESCA”) with the instrumentin a retardation mode with the analyzer at fixed band pass energy(constant resolution). The analysis entails irradiation of the samplewith soft X-rays, e.g., Al K_(α) (1486.6 eV), whose energy is sufficientto ionize core and valence electrons. The ejected electrons leave thesample with a kinetic energy that equals the difference between theexciting radiation and the “binding energy” of the electron (ignoringwork function effects). Because only the elastic electrons, i.e., thosethat have not undergone energy loss by any inelastic event, are measuredin the photoelectron peak, and because the inelastic mean free path ofelectrons in solids is short, ESCA is inherently a surface sensitivetechnique. The kinetic energy of the electrons is measured using anelectrostatic analyzer and the number of electrons are determined usingan electron multiplier. The data are presented as the number ofelectrons detected versus the binding energy of the electrons. ESCAsurvey spectra were taken using monochromatic Al K_(α) x-rays forexcitation of the photoelectrons with the analyzer set for a 117 eV bandpass energy. The X-ray source was operated at 40 watts power and datawere collected from the 200 μm spot on the sample being irradiated.These conditions give high sensitivity but low energy resolution. Thespectra were accumulated taking a 1.0 eV step size across the regionfrom 1100 eV to 0 eV and co-adding repetitive scans to achieveacceptable signal/noise in the data. The elements present wereidentified and quantified using the standard data processing andanalysis procedures provided with the instrumentation by the vendor.From the relative intensities of the photoelectron peaks, the relativeatomic concentrations of the elements Pt/C/O are obtained. ESCA analysisis generally cited as having a precision of ±20% using tabulatedresponse factors for a particular instrument configuration.

Table 5 shows the C/O and O/Pt ratios at the surface of each freshcatalyst, and the amount of leaching for each of the catalysts during asingle-cycle PMIDA oxidation reaction. TABLE 5 Effects of C/O and O/PtRatios During PMIDA Oxidation¹ Reduction Pt in Treatment C/O O/Pt Soln.CH₂O Catalyst After Depositing Ratio Ratio (μg/g)² (mg/g)³ 5% on NaBH₄23.7 3 ND⁴ deoxygentated Reduced carbon⁵ same Pt (II)⁶ 35.3 17 1.2 24.44640° C./9 hr/10% H₂ same NaBH₄ Reduced 21.1 3 6.9 Aldrich Cat. 640° C./6hr/20% H₂ 67.9 3 5.2 13.78 No. 33015-9 same 75° C./6 hr/20% H₂ 13.4 1027.5 19.85 same Used as Received 13.3 10 42.6 19.39 Aldrich Cat. 640°C./6 hr/20% H₂ 45.2 7 10.5 21.90 #20593-1 NH₃ wash/pH = 11 same 640°C./6 hr/20% H₂ 37.7 10 10.5 14.60 same Used as Received 9.1 26 32.332.96 5% Pt on 640° C./7 hr/20% H₂ 6.7 8 19.3 20.79 SA-30 NH₃ wash/pH =9.5 Westcavo carbon same 640° C./8 hr/20% H₂ 63.3 8 30.9 19.67 same 75°C./7 hr/20% H₂ 13.2 32 81.3 48.52¹The reaction conditions were the same as those used in Example 5.²μg Pt which leached into solution per gram Glyphosate produced.³mg formaldehyde per gram Glyphosate produced.⁴“ND” means none detected.⁵The carbon support was deoxygenated using the singe-stephigh-temperature deoxygenation technique #2 described in Example 2.⁶The Pt was deposited using diamminedinitrito P(II) as described inExample 11.

Example 8 Analysis of Catalyst Surface Using Thermogravimetric Analysiswith In-Line Mass Spectroscopy (TGA-MS)

The concentration of oxygen-containing functional groups at the surfacesof various fresh catalysts was determined by thermogravimetric analysiswith in-line mass spectroscopy (TGA-MS) under helium. To perform thisanalysis, a dried sample (100 mg) of fresh catalyst is placed into aceramic cup on a Mettler balance. The atmosphere surrounding the samplethen is purged with helium using a flow rate 150 ml/min. at roomtemperature for 10 minutes. The temperature subsequently is raised at10° C. per minute from 20° to 900° C., and then held at 900° C. for 30minutes. The desorptions of carbon monoxide and carbon dioxide aremeasured by an in-line mass spectrometer. The mass spectrometer iscalibrated in a separate experiment using a sample of calcium oxalatemonohydrate under the same conditions.

Table 6 shows the amount of carbon monoxide desorbed per gram of eachcatalyst using TGA-MS, and the amount of leaching for each of thecatalysts during a single-cycle PMIDA oxidation reaction using the samereaction conditions as in Example 5. As Table 6 shows, leaching tends todecrease as the amount of CO desorption decreases, and is particularlylow when the desorption is no greater than 1.2 mmole/g (mmole COdesorbed per gram of catalyst). TABLE 6 Effects of Oxygen-ContainingFunctional Groups Which Desorb from Catalyst Surface as CO during TGA-MSReduction TGA-MS Pt in Soln. CH₂O Catalyst Treatment (mmole/g)¹ (μg/g)²(mg/g)³ Aldrich Cat. 640° C./6 hr/20% H₂ 0.41 5.2 13.78 #33015-9 same640° C./6 hr/20% H₂ 0.38 5.3 15.70 NH₃ wash/pH = 9.5 same 75° C./6hr/20% H₂ 1.87 27.5 19.85 same NH₃ wash/pH = 9.5 1.59 40.7 22.73 sameUsed as Received 1.84 42.6 19.39¹mmole of CO per gram of catalyst²μg of noble metal which leaches into solution per gram of Glyphosateproduced³mg of formaldehyde per gram of Glyphosate produced

Example 9 Effect of Temperature During High-Temperature Gas-PhaseReduction

This example demonstrates the effects of using various temperatures whenheating the catalyst in the presence of a reducing agent.

An unreduced catalyst having 5% platinum on an activated carbon support(which was deoxygenated using the single-step high-temperaturedeoxygenation technique #2 described in Example 2 before the platinum isdeposited) was heated at various temperatures in 10% H₂ and 90% argonfor about 2 hours. The catalyst then was used to catalyze the PMIDAoxidation reaction. The reaction was conducted in a 250 ml glass reactorusing 5 g PMIDA, 0.157% catalyst (dry basis), 200 g total reaction mass,a temperature of 80° C., a pressure of 0 psig, and an oxygen flow rateof 150 ml/min.

The results are shown in Table 7. Increasing the reduction temperaturefrom 125° C. to 600° C. reduces the amount of noble metal leaching andincreases the formaldehyde oxidation activity during the oxidationreaction of PMIDA into Glyphosate. TABLE 7 Effects of ReductionTemperature Reduction Temperature Pt in Soln. CH₂O C/O O/Pt (° C.)(normalized¹) (normalized²) Ratio Ratio 125 1.00 0.41 26 13 200 0.440.80 27 14 400 0.18 0.93 42 10 500 0.14 0.95 32 14 600 0.06 1.00 40 11¹A normalized value of 1.00 corresponds to the highest amount of Ptobserved in solution during this experiment.²A normalized value of 1.00 corresponds to the highest formaldehydeactivity during this experiment.

Example 10 Washing the Catalyst with Ammonia

An unreduced catalyst (6.22 g) consisting of 5% platinum on an activatedcarbon support (which was deoxygenated using the single-stephigh-temperature deoxygenation technique #2 described in Example 2before the platinum was deposited onto the support) was slurried in 500ml of water for 30 minutes. Afterward, the pH of the slurry was adjustedto 9.5 with diluted aqueous ammonia, and the slurry was stirred for onehour, with aqueous ammonia being periodically added to maintain the pHat 9.5. The resulting slurry was filtered and washed once with about 300ml of water. The wet cake then was dried at 125° C. under vacuum forabout 12 hours. This catalyst was heated at 640° C. for 11 hours in 10%H₂ and 90% argon, and then compared with two other catalysts consistingof 5% platinum on NUCHAR activated carbon: (a) one reduced at roomtemperature with NaBH₄ (see Example 12 for protocol), and (b) one heatedat 640° C. in 10% H₂ and 90% argon for 11 hours. The reactions were thesame as those in Example 5.

The results are shown in Table 8. Platinum leaching was the lowest withthe catalyst which was washed with ammonia before high-temperaturehydrogen reduction. TABLE 8 Effects of Ammonia Washing CH₂O HCO₂H NMG Ptin soln. Catalyst (mg/g)¹ (mg/g) (mg/g) (μg/g) NH₃-washed, 10.62 28.790.83 0.50 High-Temp., H₂-reduced High-temp., 14.97 27.82 1.38 4.64H₂-reduced Room-Temp., 28.51 70.16 2.59 8.64 NaBH₄-reduced¹These quantities are per gram Glyphosate produced.

Example 11 Use of a Less Oxidizing Noble Metal Precursor

Platinum was deposited on an activated carbon support usingdiamminedinitrito platinum (II). Approximately 20 g of an activatedcarbon support was deoxygenated using the single-step high-temperaturedeoxygenation technique #2 described in Example 2. Next, it was slurriedin 2 L of water for 2 hours. Approximately 51.3 g of a 3.4% solution ofdiamminedinitrito platinum (II), diluted to 400 g with water, then wasadded dropwise over a period of 3-4 hours. After addition was complete,stirring was continued for 90 more minutes. The pH was re-adjusted to10.5 by adding diluted aqueous NaOH, and stirring was conducted for10-14 more hours. The slurry then was filtered and washed with aplentiful amount of water until the filtrate reached constantconductivity. The wet cake was dried at 125° C. under vacuum for 10-24hours. The resulting catalyst was heated at 640° C. for 4-6 hours in 10%H₂ and 90% argon.

A control was prepared using H₂PtCl₆ to deposit platinum onto the samecarbon. The control was heated under the same conditions as the catalystprepared using diamminedinitrito platinum (II).

These catalysts were compared while catalyzing the PMIDA oxidationreaction. The reaction conditions were the same as those in Example 5.

The catalyst prepared using diamminedinitrito platinum (II) showed lessleaching than the control. Only 1.21 μg platinum per gram of Glyphosateproduced leached into solution, which was about three times better thanthe control.

Example 12 Reducing the Catalyst Surface Using NaBH₄

The purpose of this example is to demonstrate the effects of reducingthe catalyst using NaBH₄.

Approximately 5 g of an activated carbon support (which was deoxygenatedusing the single-step high-temperature deoxygenation technique #2described in Example 2 before the platinum was deposited onto thesupport) was slurried with 85 ml of distilled water in a 250 ml roundbottom flask. The slurry was stirred in a vacuum for about 1 hour. Next,0.706 g of H₂PtCl₆ in 28 ml of distilled water was added to the slurryat a rate of about 1 ml per 100 seconds with the vacuum still beingapplied. After stirring overnight in the vacuum, the reactor was broughtto atmospheric pressure by admitting a flow of N₂. After allowing theslurry to settle, approximately 30 ml of colorless supernatant wasdecanted. The remaining slurry was transferred to a 100 ml Teflon roundbottom. At this point, the pH was adjusted to 12.2 with 0.3 g of NaOH.Then, 2.3 ml of NaBH₄ in 14 M NaOH was added at 0.075 ml/min.Subsequently, the resulting slurry was stirred for one hour, filtered,and washed five times with 50 ml of distilled water. The catalyst thenwas dried at 125° C. and 6 mmHg for 12 hours.

The resulting catalyst was used to catalyze the PMIDA oxidation. Thereaction was conducted in a 300 ml stainless steel reactor using 0.5%catalyst, 8.2% PMIDA, a total reaction mass of 180 g, a pressure of 65psig, a temperature of 90° C., an agitation rate of 900 rpm, and anoxygen feed rate of 72 ml/min.

A control experiment also was conducted at the same reaction conditionsusing 5.23% platinum on an activated carbon support (which wasdeoxygenated using the single-step high-temperature deoxygenationtechnique #2 described in Example 2 before the platinum was depositedonto the support).

Table 9 shows the results using the NaBH₄-reduced catalyst, and Table 10shows the results of the control experiment. Reducing with NaBH₄ reducedthe amount of noble metal leaching. It also reduced the amount offormaldehyde and NMG after a period of use. TABLE 9 Results UsingCatalyst Treated with NaBH₄ Run # 1 2 3 4 5 6 Glyphosate (%) 5.79 5.815.75 5.74 5.79 5.77 PMIDA (%) 0.23 0.08 0.13 0.22 0.13 0.13 CH₂O (mg/gglyph) 28.5 31.5 47.8 38.8 41.6 45.8 HCO₂H (mg/g glyph) 70.2 90.5 100.596.6 98.8 99.0 AMPA/MAMPA (%) 0.02 0.01 0.01 0.01 0.01 0.01 NMG (mg/gglyph) 2.6 3.6 3.6 4.2 4.7 4.7 Pt. in Soln. 8.64 8.60 5.22 6.96 6.915.20 (μg/g glyph.) % of Pt Lost 0.20 0.20 0.12 0.16 0.16 0.12

TABLE 10 Results Using Catalyst which was not treated with NaBH₄ Run # 12 3 4 5 6 Glyphosate (%) 5.36 5.63 5.37 5.50 5.56 5.59 PMIDA (%) 0.180.15 0.25 0.21 0.18 0.23 CH₂O (%) 20.9 23.6 38.4 44.2 47.7 58.3 HCO₂H(%) 27.8 63.8 96.5 98.4 102.2 102.0 AMPA/MAMPA (%) 0.04 0.02 0.04 0.020.02 0.03 NMG (mg/g glyph) 1.5 3.0 5.4 6.9 10.6 7.3 Pt. in Soln. 63.662.2 44.7 34.6 28.8 28.6 (μg/g glyph.) % of Pt Lost 1.30 1.34 0.92 0.730.61 0.61

Example 13 Use of Bismuth as a Catalyst-Surface Promoter

A 500 g solution was prepared consisting of 10⁻³ M Bi(NO₃)₃.5H₂O in 10⁻³M formic acid solution. This solution was added to 500 g of a 5%formaldehyde solution containing 6.0 g of 5% platinum on an activatedcarbon support. The solution was stirred at 40° C. under N₂ overnightand then filtered with a Buchner funnel. An aliquot was dried andsubsequently analyzed by X-ray fluorescence. The catalyst had a loss ondrying (“LOD”) of 63%. The dry catalyst was found to containapproximately 3% bismuth and 4% platinum.

The following were placed into a 300 ml stainless steel autoclave: 16.4g of PMIDA; 4.16 g of an activated carbon catalyst, 0.68 g of the abovecatalyst consisting of 3% bismuth/4% platinum on its surface, and 179.4g of water. The reaction was conducted at a pressure of 65 psig, atemperature of 90° C., an oxygen flow rate of 38 ml/min., and a stirrate of 900 rpm. The reaction was allowed to proceed until the PMIDA wasdepleted. The product solution was separated from the catalyst viafiltration and the solution was neutralized with 6 g of 50% NaOHsolution. The catalyst was recycled with no purge through 5 runs.Analysis of the product solution was done for each run. Two controlsalso were conducted in the same manner as above except that the 0.68 gof the Bi/Pt/carbon catalyst was omitted.

The results are shown in Table 11. The runs having the Bi/Pt/carboncatalyst produced lower levels of formaldehyde, formic acid, and NMG inthe product. TABLE 11 PMIDA Oxidation Results Using Pt/Bi/C CatalystCONTROL CONTROL #1 #2 1ST RUN 2ND RUN 3RD RUN 4TH RUN 5TH RUN Glyphosate(%) 5.7 5.59 5.69 5.72 5.87 5.74 5.68 PMIDA (%) ND ND 0.04 0.07 0.0850.04 0.046 AMPA (%) 0.034 0.031 0.015 0.009 0.008 DBNQ¹ DBNQ CH₂O (mg/gglyph. 142 138 28 31 34 38 42 prod.) HCO₂H (mg/g glyph. 56 57 DBNQ 7 1417 23 prod.) AMPA/MAMPA (%) 0.047 0.041 0.021 0.014 0.013 0.014 0.013NMG (mg/g glyph. 16.3 19.3 0.7 0.9 1.4 2.3 2.6 prod.)¹DBNQ = detectable, but not quantitated.

Example 14 Depositing a Tin Promoter on a Carbon Support

An activated carbon (20 g) was slurried in about 2 L of water. Next,0.39 g of SnCl₂.2H₂O was dissolved in 500 g of 0.5% HNO₃. The solutionwas added dropwise to the carbon slurry. After all the solution wasadded, the slurry was stirred for 2 hours. The pH then was adjusted to9.5, and the slurry was stirred for a few more hours. Next, the slurrywas filtered and washed with a plentiful amount of water until thefiltrate reached a constant conductivity. The wet cake was dried at 125°C. under vacuum to give 1% tin on carbon. Following drying, the 1% tinon carbon was calcined in argon at 500° C. for 6 hours.

To deposit platinum onto the carbon support, 5 g of the 1% tin on carbonfirst was slurried in about 500 ml of water. Then 0.705 g of H₂PtCl₆ wasdissolved in about 125 ml of water and added dropwise. After all theH₂PtCl₆ solution was added, the slurry was stirred for 2.5 hours. The pHthen was adjusted to 9.5 with diluted NaOH and stirring was continuedfor a few more hours. The slurry then was filtered and washed with aplentiful amount of water until the filtrate reached constantconductivity. The wet cake was dried at 125° C. under vacuum.

This technique produced a catalyst comprising 5% platinum and 1% tin oncarbon.

Example 15 Depositing an Iron Promoter onto a Carbon Support

Approximately 5 g of activated carbon was slurried in about 500 ml ofwater. Next, 0.25 g of FeCl₃.6H₂O was dissolved in 75 ml of water. Thesolution was added dropwise to the carbon slurry. After all the solutionwas added, the slurry was stirred for two hours. The slurry then wasfiltered and washed with a plentiful amount of water until the filtratereached a constant conductivity. The wet cake was dried at 125° C. undervacuum to give 1% iron on carbon. Following drying, the 1% iron oncarbon was calcined in argon at about 500° C. for 8 hours.

To deposit platinum onto the surface of the carbon support, 2.5 g of the1% iron on carbon first was slurried in about 180 ml of water. Then,0.355 g of H₂PtCl₆ was dissolved in about 70 ml of water and addeddropwise. After all the solution was added, the slurry was stirred forthree more hours. The pH then was adjusted to about 10.0 with dilutedNaOH and stirring was continued for a few more hours. Next, the slurrywas filtered and washed with a plentiful amount of water until thefiltrate reached a constant conductivity. The wet cake was dried at 125°C. under vacuum.

This technique produces a catalyst comprising 5% platinum and 1% iron oncarbon.

Example 16 Effect of Presence of Noble Metal on the Surface of theCarbon Support

This example shows the advantages of using a carbon support having anoble metal on its surface for effecting the oxidation of PMIDA ratherthan a carbon-only catalyst having no noble metal on its surface.

The PMIDA oxidation reaction was conducted in the presence of acarbon-only catalyst which was deoxygenated using the single-stephigh-temperature deoxygenation technique #2 described in Example 2. Thereaction was carried out in a 300 ml stainless steel reactor using0.365% catalyst, 8.2% PMIDA, a total reaction mass of 200 g, a pressureof 65 psig, a temperature of 90° C., an agitation rate of 900 rpm, andan oxygen feed rate of 38 ml/min.

Table 12 shows the reaction times (i.e., the time for at least 98% ofthe PMIDA to be consumed) of 5 cycles for the carbon-only catalyst.Table 12 also shows the reaction times for the two Pt-on-carboncatalysts in Example 12 over 6 cycles under the reaction conditionsdescribed Example 12. As may be seen from Table 12, the deactivation ofthe carbon-only catalyst per cycle generally tends to be greater (i.e.,the reaction times tend to increase more per cycle) than thedeactivation of the carbon catalysts which had a noble metal on theirsurfaces. The deactivation particularly appears to be less where thecatalyst has been reduced with NaBH₄ after the noble metal was depositedonto the surface. Without being bound by any particular theory, it isbelieved that the deactivation of the catalyst reduced with NaBH₄ wasless than the deactivation of the other Pt-on-carbon catalyst becausethe platinum on the NaBH₄ catalyst leached less than the platinum on theother Pt-on-carbon catalyst. See Example 12, Tables 9 & 10. TABLE 12Results Using Catalyst which was not treated with NaBH₄ Run # 1 2 3 4 56 Run Time for 45.4 55.0 64.4 69.8 75.0 Carbon-Only Catalyst (min.) RunTime for 5% 35.1 NA¹ NA 35.2 35.8 35.8 platinum on Carbon Catalyst whichwas Reduced w/NaBH₄ (min.) Run Time for 5.23% 40.4 42.0 44.2 44.1 44.952.7 platinum on Carbon Catalyst (min.)¹Not available due to temperature problems.

Example 17 The Effect of Using a Catalyst Comprising a Noble MetalAlloyed with a Catalyst-Surface Promoter

This example shows the advantages of a catalyst comprising platinumalloyed with iron.

1. Catalyst Comprising Platinum Alloyed with Iron

To prepare the catalyst comprising platinum alloyed with iron,approximately 10 grams of an activated carbon was slurried in about 180ml of water. Next, 0.27 grams of FeCl₃.6H₂O and 1.39 grams of H₂PtCl₆hydrate were co-dissolved in about 60 ml of water. This solution wasadded dropwise to the carbon slurry over a period of about 30 minutes.During the addition, the pH of the slurry dropped and was maintained atfrom about 4.4 to about 4.8 using a dilute NaOH solution (i.e., a 1.0 to2.5 molar solution of NaOH). Afterward, the slurry was stirred for 30more minutes at a pH of about 4.7. The slurry then was heated under N₂to 70° C. at a rate of about 2° C./min. while maintaining the pH atabout 4.7. Upon reaching 70° C., the pH was raised slowly over a periodof about 30 minutes to 6.0 with addition of the dilute NaOH solution.The stirring was continued for a period of about 10 min. until the pHbecame steady at about 6.0. The slurry was then cooled under N₂ to about35° C. Subsequently, the slurry was filtered, and the cake was washedwith approximately 800 ml of water 3 times. The cake was then dried at125° C. under a vacuum. This produced a catalyst containing 5 wt. %platinum and 0.5 wt. % iron on carbon upon heating at 690° C. in 20% H₂and 80% Ar for 1-6 hr.

This catalyst was analyzed via electron microscopy, as described in moredetail in Example 19. An image obtained through TEM of the carbonsupport showed that the alloyed metal particles were highly dispersedand uniformly distributed throughout the carbon support (the white dotsrepresent the metal particles; and the variations in the backgroundintensity are believed to represent the change of the local density ofthe porous carbon). The average size of the particles was about 3.5 nm,and the average distance between particles was about 20 nm. A highenergy resolution X-ray spectra from an individual metal particle of thecatalyst showed that both platinum and iron peaks were present (thecopper peaks originated from the scattering of the copper grids).Quantitative analysis of the high energy resolution X-ray spectra fromdifferent individual metal particles showed that the composition of theparticles, within experimental error, did not vary with the size or thelocation of the metal particles on the catalyst surface.

2. Catalyst in which Platinum was Less Alloyed with Iron

To prepare the Pt/Fe/C catalyst in which the platinum was less alloyedwith iron (i.e., this catalyst has less platinum alloyed with iron thandoes the first catalyst described in this example), the platinum andiron were deposited sequentially onto the surface of the carbon support.Approximately 5 grams of an activated carbon was slurried in about 500ml of water. The pH was adjusted to about 5.0 with 1N HCl. Next, about0.25 grams of FeCl₃.6H₂O was dissolved in 75 ml of water. This solutionwas added dropwise to the carbon slurry over a period of about 60 min.After all the solution was added, the slurry was stirred for about 2hours. The pH was adjusted to 9.5 with the dilute NaOH solution, and theslurry was stirred for a few more hours. Afterward, the slurry wasfiltered and washed with a plentiful amount of water. The wet cake wasdried at 125° C. under vacuum to produce 1 wt. % iron on carbon.Following drying, this 1 wt. % iron on carbon was reduced with anatmosphere containing 20% H₂ and 80% Ar at 635° C. for 1-6 hr. About 2.5grams of this 1 wt. % iron on carbon was slurried in 250 ml of water.Next, about 0.36 grams of H₂PtCl₆ hydrate was dissolved in 65 ml ofwater, which, in turn, was added dropwise to the slurry over a period ofabout 60 min. After all the solution was added, the slurry was stirredfor 2 hours. The slurry then was filtered and washed with a plentifulamount of water. The cake was then re-slurried in 450 ml of water. Afteradjusting the pH of the slurry to 9.5 with the dilute NaOH solution, theslurry was stirred for about 45 min. Next, the slurry was filtered andwashed once with 450 ml of water. The wet cake was the dried at 125° C.under vacuum. This produced a catalyst containing 5 wt. % platinum and 1wt. % iron on carbon upon reduction by heating to a temperature of 660°C. in an atmosphere containing 20% H₂ and 80% Ar for 1-6 hr.

3. Comparison of the Two Catalysts

These two catalysts were compared while catalyzing the PMIDA oxidationreaction. The reaction conditions were the same as those in Example 5.Table 13 shows the results. The first catalyst described in this example(i.e., the catalyst comprising a greater amount of platinum alloyed withiron) had greater stability with respect to CH₂O & HCO₂H activities; thesecond catalyst described in this example (i.e., the catalyst comprisinga lower amount of platinum alloyed with iron) deactivated rapidly. Inaddition, the first catalyst retained almost half of its iron contentover 25 cycles, while the second catalyst lost most of its iron in thefirst cycle. TABLE 13 Comparison of Catalyst Having Pt/Fe Alloy withCatalyst Having Less Pt/Fe Alloy cycle cycle cycle cycle cycle 1 cycle 2cycle 3 cycle 4 cycle 5 cycle 6 cycle 7 cycle 8 cycle 9 10 11 12 13Alloyed Pt & Fe CH₂O (mg/g glyph. 10.49 9.23 6.04 4.92 4.44 5.08 5.24prod.) HCO₂H (mg/g 19.91 29.64 27.84 25.62 27.99 29.73 28.95 glyph.prod.) NMG (mg/g glyph. 0.22 0.44 0.28 0 0 0 0 prod.) Pt in soln. 5.084.87 3.6 3.06 (μg/g glyph. prod.) % of Fe Lost 44 1.9 1.2 0.8 Lessalloyed Pt & Fe CH₂O (mg/g glyph. 10.16 10.7 12.24 13.56 14.68 prod.)HCO₂H (mg/g 27.23 37.72 45.01 54.57 61.14 glyph. prod.) NMG (mg/g glyph.0 0.98 1.23 1.77 2 prod.) Pt in soln. 3.83 3.36 3.54 3.44 3.32 (μg/gglyph. prod.) % of Fe Lost 86 3.2 1.4 1.8 1.4

Example 18 Preparation of a Pt/Fe/Sn on Carbon Catalyst

Approximately 10 grams of an activated carbon was slurried in about 90ml of water. Next, about 0.2 g of SnCl₂.2H₂O was dissolved in 250 ml of0.025 M HCl. The solution was added dropwise to the carbon slurry. Afterall the solution was added, the slurry was stirred for 3 hr. The pH thenwas slowly adjusted to 9.0 with a diluted NaOH solution (i.e., a 1.0 to2.5 molar solution of NaOH), and the slurry was stirred for a few morehours. Next, the slurry was filtered and washed with a plentiful amountof water until the filtrate reached a constant conductivity. The wetcake was dried at 125° C. under vacuum. This produced 0.9 wt. % tin oncarbon. About 6 grams of this 0.9 wt. % tin on carbon was slurried inabout 500 ml of water. Then approximately 0.23 grams of Fe(NO₃)₃.9H₂Oand 0.85 grams of H₂PtCl₆ were co-dissolved in about 150 ml of water andadded dropwise to the slurry. After all the solution was added, theslurry was stirred for 4 hours, and then filtered to remove excess iron(˜80 wt. %). The wet cake was re-slurried in 480 ml of water. After thepH of the slurry was adjusted to 9-10 with the dilute NaOH solution, theslurry was stirred for a few more hours. Next, the slurry was filteredand washed with a plentiful amount of water until the filtrate reached aconstant conductivity. The wet cake was dried at 125° C. under vacuum.This produced a catalyst containing 4.9 wt. % Pt, 0.9 wt. % tin and 0.1wt. % iron on carbon upon high-temperature reduction by heating at700-750° C. in 20% H₂ and 80% Ar for 1-6 hr.

Example 19 Electron Microscopy Characterization of Catalysts

Electron microscopy techniques were used to analyze the size, spatialdistribution, and composition of the metal particles of catalystsprepared in Example 17. Before analyzing the catalyst, the catalyst wasfirst embedded in an EM Bed 812 resin (Electron Microscopy Sciences,Fort Washington, Pa.). The resin was then polymerized at about 60° C.for approximately 24 hr. The resulting cured block was ultramicrotomedinto slices having a thickness of about 50 nm. These slices were thentransferred to 200 mesh copper grids for electron microscopyobservation.

High-resolution analytical electron microscopy experiments were carriedout in a Vacuum Generators dedicated scanning transmission electronmicroscope (model no. VG HB501, Vacuum Generators, East Brinstead,Sussex, England) with an image resolution of less than 0.3 nm. Themicroscope was operated at 100 kV. The vacuum in the specimen chamberarea was below about 10⁻⁶ Pa. A digital image acquisition system (ESVision Data Acquisition System, EmiSpec Sys., Inc., Tempe, Ariz.) wasused to obtain high-resolution electron microscopy images. A windowlessenergy dispersive X-ray spectrometer (Link LZ-5 EDS Windowless Detector,Model E5863, High Wycombe, Bucks, England) was used to acquire highenergy resolution X-ray spectra from individual metal particles. Becauseof its high atomic-number sensitivity, high-angle annular dark-field(HAADF) microscopy was used to observe the metal particles. An electronprobe size of less than about 0.5 nm was used to obtain the HAADFimages, and a probe size of less than about 1 nm was used to obtain highenergy resolution X-ray spectra.

Example 20 Effect of a Supplemental Promoter

This example shows the use and advantages of mixing a supplementalpromoter with a carbon-supported, noble-metal-containing oxidationcatalyst.

A. Comparison of Effects on a PMIDA Oxidation Reaction Caused by Mixinga Carbon-Supported, Noble-Metal-Containing Catalyst with Various Amountsand Sources of Bismuth

Several single batch PMIDA oxidation reactions were conducted. In eachreaction, a different source and a different amount of bismuth wereadded to the reaction medium. The source of bismuth was either(BiO)₂CO₃, Bi(NO₃)₃.5H₂O, or Bi₂O₃. The amount of bismuth usedcorresponded to a bismuth to PMIDA mass ratio of 1:10,000; 1:2,000; or1:1,000. A control was also conducted wherein no bismuth was added.

Each PMIDA oxidation reaction was conducted in the presence of acatalyst containing 5% by weight platinum and 0.5% by weight iron (thiscatalyst was prepared using a method similar to that described inExample 17). The reaction was carried out in a 1000 ml stainless steelreactor (Autoclave Engineers, Pittsburgh, Pa.) using 2.5 g catalyst(0.5% by weight of the total reaction mass), 60.5 g PMIDA (12.1% byweight of the total reaction mass), 1000 ppm formaldehyde, 5000 ppmformic acid, a total reaction mass of 500 g, a pressure of 110 psig, atemperature of 100° C., and an agitation rate of 1000 rpm. The oxygenfeed rate for the first 22 minutes was 392 ml/min., and then 125 ml/min.until the PMIDA was essentially depleted.

Table 14 shows the results. In all the runs where a bismuth compound wasadded, the formaldehyde, formic acid, and NMG levels were less thanthose observed in the control. TABLE 14 Direct Addition of VariousSources and Amounts of Bismuth Amt. & AMPA/ Run source of Glyph. PMIDACH₂O HCO₂H MAMPA NMG Time Bi Added (%)** (%)** (mg/g)*** (mg/g)***(mg/g)*** (mg/g)*** (min.) 0 (control) 8.2 ND 4.0 22.5 9.4 2.0 39.30.0074 g 8.1 ND 2.6 3.8 10.9 ND 54.1 (BiO)₂CO₃ (100 ppm*) 0.037 g 7.8 ND1.8 1.4 14.5 ND 58.2 (BiO)₂CO₃ (500 ppm) 0.074 g 7.7 ND 2.0 1.3 16.4 ND60.2 (BiO)₂CO₃ (1000 ppm) 0.0141 g 8.1 ND 2.4 3.0 11.2 ND 53.2Bi(NO₃)₃•5H₂O (100 ppm) 0.070 g 7.7 ND 1.9 1.4 14.4 ND 58.5Bi(NO₃)₃•5H₂O (500 ppm) 0.141 g 7.6 ND 2.0 1.2 16.2 ND 59.2Bi(NO₃)₃•5H₂O (1000 ppm) 0.0067 g 8.1 ND 2.5 3.5 13.9 ND 48 Bi₂O₃ (100ppm) 0.034 g 7.6 ND 2.0 1.4 15.1 ND 58.7 Bi₂O₃ (500 ppm) 0.067 g 7.6 ND2.0 1.2 17.3 ND 60.6 Bi₂O₃ (1000 ppm)*ppm means a ratio of Bi to PMIDA equaling 1:1,000,000**(mass ÷ total reaction mass) × 100%***mg ÷ grams of glyphosate produced“ND” means none detectedB. Effect of Bismuth Addition on Subsequent PMIDA Oxidation BatchesContacted with the Catalyst

Four 6-run experiments (i.e., during each of the 4 experiments, 6 batchreactions were conducted in sequence) were conducted to determine theeffect of (1) the initial bismuth addition on reaction runs subsequentto the initial bismuth addition, and (2) adding additional bismuth inone or more of the subsequent reaction runs.

All 4 experiments were conducted using a catalyst containing 5% byweight platinum and 0.5% by weight iron (this catalyst was preparedusing a method similar to that described in Example 17). During each6-run experiment, the same catalyst was used in each of the 6 runs(i.e., after the end of a run, the reaction product solution wasseparated and removed from the catalyst, and a new batch of PMIDA wasthen combined with the catalyst to begin a new run). The reaction wascarried out in a 1000 ml stainless steel reactor (Autoclave Engineers)using 2.5 g catalyst (0.5% by weight of the total reaction mass), 60.5 gPMIDA (12.1% by weight of the total reaction mass), 1000 ppmformaldehyde, 5000 ppm formic acid, a total reaction mass of 500 g, apressure of 110 psig, a temperature of 100° C., and an agitation rate of1000 rpm. The oxygen feed rate for the first 22 minutes was 392 ml/min.,and then 125 ml/min. until the PMIDA was essentially depleted.

In the control experiment, no bismuth was introduced into the reactionzone during any of the 6 runs. In the three other experiments, 0.034grams of bismuth(III) oxide (i.e., Bi₂O₃) were introduced into thereaction medium at the beginning of the first reaction run. In one ofthese experiments, the bismuth oxide was only introduced into thereaction zone at the beginning of the first reaction run. In anotherexperiment, 0.034 g of bismuth(III) oxide was introduced into thereaction medium at the beginning of the first and fourth reaction runs.In the final experiment, 0.034 g of bismuth(III) oxide was introducedinto the reaction medium at the beginning of all 6 reaction runs.

Tables 15, 16, 17, and 18 show the results. The one-time addition of thebismuth oxide (data shown in Table 16) tended to give the samebeneficial effects as adding the bismuth oxide every three runs (datashown in Table 17) or even every run (data shown in Table 18). TABLE 15Control Experiment: 6-Run PMIDA Oxidation Reaction with No BismuthAddition Sample (unless otherwise indicated, taken after approx. allPMIDA consumed) Run 1 Run 2 Run 3 Run 4 Run 5 Run 6 Glyphosate 8.2 8.48.4 8.5 8.5 8.4 (%)* PMIDA (%)* ND 0.006 0.008 ND ND ND CH₂O 3.1 2.4 2.02.6 3.2 3.8 (mg/g)** HCO₂H 16 23 22 25 30 40 (mg/g)** AMPA/ 7.5 6.9 6.35.5 5.8 5.9 MAMPA (mg/g)** NMG (mg/g)** 0.5 1.7 1.4 1.6 2.8 4.9 Time(min.) 48.5 43.5 54.5 52.8 54.1 51.7*(mass ÷ total reaction mass) × 100%**mg ÷ grams of glyphosate producedND means none detected

TABLE 16 6-Run PMIDA Oxidation Reaction with Bismuth Addition atBeginning of First Run Sample (unless otherwise indicated, taken afterapprox. all PMIDA consumed) Run 1 Run 2 Run 3 Run 4 Run 5 Run 6Glyphosate 7.8 8.6 8.5 8.6 8.6 7.7 (%)* PMIDA (%)* ND ND ND ND ND 0.005CH₂O 2.4 2.7 2.1 2.6 3.1 3.9 (mg/g)** HCO₂H DBNQ DBNQ DBNQ DBNQ DBNQDBNQ (mg/g)** AMPA/ 15 11 10 9.9 8.6 10 MAMPA (mg/g)** NMG (mg/g)** NDND ND ND ND ND Time (min.) 60.1 62.4 64.1 62.6 66.9 62*(mass ÷ total reaction mass) × 100%**mg ÷ grams of glyphosate producedND means none detectedDBNQ means detected, but not quantified

TABLE 17 6-Run PMIDA Oxidation Reaction with Bismuth Addition atBeginning of 1st and 4th Runs Sample (unless otherwise indicated, takenafter approx. all PMIDA consumed) Run 1 Run 2 Run 3 Run 4 Run 5 Run 6Glyphosate 7.8 8.4 8.5 8.5 8.5 8.6 (%)* PMIDA (%)* ND ND ND ND ND NDCH₂O 2.3 2.6 2.6 3.2 3.6 3.5 (mg/g)** HCO₂H 3.4 3.1 3.2 2.9 3.3 3.5(mg/g)** AMPA/ 14 11 10 11 9.3 8.9 MAMPA (mg/g)** NMG (mg/g)** ND ND NDND ND ND Time (min.) 57.4 63.2 64.3 64.9 66 64.5*(mass ÷ total reaction mass) × 100%**mg ÷ grams of glyphosate producedND means none detected

TABLE 18 6-Run PMIDA Oxidation Reaction with Bismuth Addition atBeginning of Every Run Sample (unless otherwise indicated, taken afterapprox. all PMIDA consumed) Run 1 Run 2 Run 3 Run 4 Run 5 Run 6Glyphosate 7.8 8.5 8.2 8.3 8.3 8.3 (%)* PMIDA (%)* ND ND ND ND ND NDCH₂O 2.4 2.8 3.2 2.9 3.4 4.0 (mg/g)** HCO₂H ND ND ND ND ND ND (mg/g)**AMPA/ 14 12 11 12 10 9.7 MAMPA (mg/g)** NMG (mg/g)** ND ND ND ND ND NDTime (min.) 56.4 62.4 64.8 62.8 66 66.1*(mass ÷ total reaction mass) × 100%**mg ÷ grams of glyphosate producedND means none detectedC. Effect of a One-Time Bismuth Addition Over 20 PMIDA Oxidation RunsUsing a Platinum/Iron/Carbon Catalyst

Two 20-run experiments were conducted to determine the effect of aone-time bismuth addition on 20 PMIDA oxidation reaction runs.

Both experiments were conducted using a catalyst containing 5% by weightplatinum and 0.5% by weight iron (this catalyst was prepared using asimilar method to the method described in Example 17). During eachexperiment, the same catalyst was used in each of the 20 runs. Thereaction was carried out in a 1000 ml stainless steel reactor (AutoclaveEngineers) using 2.5 g catalyst (0.5% by weight of the total reactionmass), 60.5 g PMIDA (12.1% by weight of the total reaction mass), 1000ppm formaldehyde, 5000 ppm formic acid, a total reaction mass of 500 g,a pressure of 110 psig, a temperature of 100° C., and an agitation rateof 1000 rpm. The oxygen feed rate for the first 22 minutes was 392ml/min., and then 125 ml/min. until the PMIDA was essentially depleted.In the control experiment, no bismuth was introduced into the reactionzone during any of the 20 runs. In the other experiment, 0.034 grams ofbismuth(III) oxide was introduced into the reaction medium at thebeginning of the first reaction run.

FIG. 3 compares the resulting formic acid concentration profiles. Theone-time introduction of bismuth into the reaction zone decreased theformic acid concentration over all 20 runs.

D. Effect of a One-Time Bismuth Addition Over 30 PMIDA Oxidation RunsUsing a Platinum/Tin/Carbon Catalyst

Two 30-run experiments were conducted to determine the effect of aone-time bismuth addition on 30 PMIDA oxidation reaction runs.

Both experiments were conducted using a catalyst containing 5% by weightplatinum and 1% by weight tin (this catalyst was prepared using a methodsimilar to that described in Example 18). During each experiment, thesame catalyst was used in each of the 30 runs. Each run was carried outin a 300 ml reactor (made of alloy metal, Hastelloy C, AutoclaveEngineers) using 1.35 g catalyst (0.75% by weight of the total reactionmass), 21.8 g PMIDA (12.1% by weight of the total reaction mass), 1000ppm formaldehyde, 5000 ppm formic acid, a total reaction mass of 180 g,a pressure of 90 psig, a temperature of 100° C., and an agitation rateof 900 rpm. The oxygen feed rate for the first 26 minutes was 141ml/min., and then 45 ml/min. until the PMIDA was essentially depleted.In the control experiment, no bismuth was introduced into the reactionzone during any of the 30 runs. In the other experiment, 0.012 grams ofbismuth (III) oxide was introduced into the reaction medium at thebeginning of the first reaction run.

FIG. 3 compares the resulting formic acid concentration profiles, FIG. 5compares the resulting formaldehyde concentration profiles, and FIG. 6compares the resulting NMG concentration profiles. Even after 30 runs,the one-time introduction of bismuth into the reaction zone decreasedthe formic acid concentration by 98%, the formaldehyde concentration by50%, and the NMG concentration by 90%.

E. Effect of Adding Bismuth to a Pt/Fe/C Catalyst that was PreviouslyUsed in 132 Batch PMIDA Oxidation Reactions

A 14-run experiment was conducted to determine the effect mixing bismuthwith a used Pt/Fe/C catalyst. Before this experiment, the catalyst hadbeen used to catalyze 129 batch PMIDA oxidation reactions. The freshcatalyst (i.e., the catalyst before it was used in the previous 129PMIDA oxidation runs) was prepared using a method similar to the methoddescribed in Example 17, and contained 5% by weight platinum and 0.5% byweight iron.

The 14 PMIDA oxidation reaction runs were carried out in a 300 mlreactor (made of alloy metal, Hastelloy C, Autoclave Engineers) using0.9 g of spent catalyst (0.5% by weight), 21.8 g PMIDA (12.1% byweight), 1000 ppm formaldehyde, 5000 ppm formic acid, a total reactionmass of 180 g, a pressure of 90 psig, a temperature of 100° C., and anagitation rate of 900 rpm. The oxygen feed rate for the first 26 minuteswas 141 ml/min., and then 45 ml/min. until the PMIDA was essentiallydepleted. At the beginning of the 4th run, 0.012 grams of bismuth(III)oxide was introduced into the reaction zone.

FIG. 7 shows the effects that the bismuth addition at the 4th run had onthe formic acid, formaldehyde, and NMG byproduct production.

F. Effect of Adding Bismuth to a Pt/Sn/C Catalyst that was PreviouslyUsed in 30 Batch PMIDA Oxidation Reactions

An 11-run experiment was conducted to determine the effect of mixingbismuth with a used Pt/Sn/C catalyst. The catalyst had previously beenused to catalyze 30 batch PMIDA oxidation reactions. The fresh catalyst(i.e., the catalyst before it was used in the previous 30 PMIDAoxidation runs) was prepared using a method similar to that described inExample 18, and contained 5% by weight platinum and 1% by weight tin.

The 11 PMIDA oxidation reaction runs were carried out in a 300 mlreactor (made of alloy metal, Hastelloy C, Autoclave Engineers) using1.35 g of used catalyst (0.75% by weight of the total reaction mass),21.8 g PMIDA (12.1% by weight of the total reaction mass), 1000 ppmformaldehyde, 5000 ppm formic acid, a total reaction mass of 180 g, apressure of 90 psig, a temperature of 100° C., and an agitation rate of900 rpm. The oxygen feed rate for the first 26 minutes was 141 ml/min.,and then 45 ml/min. until the PMIDA was essentially depleted. At thebeginning of the 4th run, 0.012 grams of bismuth(III) oxide wasintroduced into the reaction zone.

FIG. 8 shows the effects that the bismuth addition at the 4th run had onthe formic acid, formaldehyde, and NMG byproduct production.

G. Effect of Bismuth Addition on Over 100 Subsequent PMIDA OxidationBatches Contacted with the Catalyst

Two 125-run experiments were conducted to determine the effect ofbismuth addition on over 100 subsequent reaction runs using the samecatalyst.

Both experiments were conducted using a catalyst containing 5% by weightplatinum and 1% by weight tin (this catalyst was prepared using a methodsimilar to that described in Example 18). During each experiment, thesame catalyst was used in all the runs. The reaction was carried out ina stirred-tank reactor using 0.75% catalyst (by weight of the totalreaction mass), 12.1% PMIDA (by weight of the total reaction mass), apressure of 128 psig, and a temperature of 100° C. The oxygen feed ratefor the first part of each batch reaction (the exact amount of timevaried with each batch from 14.9 to 20.3 minutes, with times closer to14.9 minutes being used for the earlier batches, and times closer to20.3 minutes being used for the later batches) was 1.3 mg/min. per gramtotal reaction mass, and then 0.35 mg/min. per gram total reaction massuntil the PMIDA was essentially depleted. A portion of the reactionproduct from each batch was evaporated off and returned to the reactoras a source of formaldehyde and formic acid to act as sacrificialreducing agents in the next batch reaction. The amounts of formaldehydeand formic acid recycled back to the reactor ranged from 100 to 330 ppm,and from 0 ppm to 2300 ppm (0 to 200 ppm formic acid after 25 batchesfollowing the addition of bismuth(III) oxide), respectively.

In the control experiment, no bismuth was introduced into the reactionzone during any of the 125 runs. In the other experiment, the catalystwas first used to catalyze 17 batches of PMIDA. After catalyzing the17th batch, the catalyst was substantially separated from the reactionproduct, and the resulting catalyst mixture was transferred to acatalyst holding tank where 9.0 mg of bismuth(III) oxide per gram ofcatalyst were introduced into the catalyst mixture. The catalyst wasthen used to catalyze the oxidation of 107 subsequent batches of PMIDA.

FIG. 9 compares the resulting formic acid concentration profiles, FIG.10 compares the resulting formaldehyde concentration profiles, and FIG.11 compares the resulting NMG concentration profiles. Even after 107runs, the one-time introduction of bismuth into a mixture with thecatalyst decreased the formic acid and NMG concentrations by roughly90%.

Example 21 Evaluation of Cadmium, Nickel, Copper, Molybdenum Arsenic andManganese as Supplemental Promoters

Fourteen single-run oxidation experiments were conducted to determinethe effects of the one-time additions of cadmium oxide, nickel oxide,copper carbonate, molybdenum oxide, arsenic oxide, and manganese oxidesalts to a PMIDA oxidation reaction.

The experiments were conducted using a catalyst containing 5% by weightplatinum and 0.5% by weight iron. Each experiment was carried out in a 1L reactor (made of stainless steel, Autoclave Engineers) using 2.5 gcatalyst (0.5% by weight of the total reaction mass), 60.5 g PMIDA(12.1% by weight of the total reaction mass), 1000 ppm formaldehyde,5000 ppm formic acid, a total reaction mass of 500 g, a pressure of 110psig, a temperature of 100° C., and an agitation rate of 900 rpm. Theoxygen feed rate for the first 22 minutes was 392 cc/min., and then 125cc/min until the PMIDA was essentially depleted. In the controlexperiment, no metal was introduced. In the other experiments, metal wasadded to the reaction medium as follows:

Experiment 1—0.034 g (60 ppm) of cadmium oxide (CdO) was added;Experiment 2—0.069 g (120 ppm) of cadmium oxide (CdO) was added;Experiment 3—0.038 g (60 ppm) of nickel(ous) oxide (NiO) was added;Experiment 4—0.076 g (120 ppm) of nickel(ous) oxide (NiO) was added;Experiment 5—0.052 g (60 ppm) of copper(II) carbonate (CuCO₂.(OH)₂) wasadded; Experiment 6—0.104 g (120 ppm) of copper(II) carbonate(CuCO₂.(OH)₂) was added; Experiment 7—0.052 g (60 ppm) of molybdenum IVoxide (MoO₂) was added; Experiment 8—0.104 g (120 ppm) of molybdenum IVoxide (MoO₂) was added; Experiment 9—0.040 g (60 ppm) of arsenic(III)oxide (As₂O₃) was added; Experiment 10—0.080 g (120 ppm) of arsenic(III)oxide (As₂O₃) was added; Experiment 11—0.043 g (60 ppm) ofmanganese(III) oxide was added; Experiment 12—0.086 g (120 ppm) ofmanganese(III) oxide was added; Experiment 13—0.046 g (60 ppm) ofarsenic(V) oxide hydrate (As₂O₅.3H₂O) was added; and Experiment 14—0.092g (120 ppm) of arsenic(V) oxide hydrate (As₂O₅.3H₂O) was added.

Results for the experiments as well as the control experiment areillustrated in Table 19. TABLE 19 Exp. No. 1 2 3 4 5 6 7 8 Metal CdO CdONiO NiO CuCO₂•(OH)₂ CuCO₂•(OH)₂ MoO₂ MoO₂ Added (60 ppm) (120 ppm) (60ppm) (120 ppm) (60 ppm) (120 ppm) (60 ppm) (120 ppm) Run Time 42.4 5755.4 55.1 64.3 67.2 62.9 54.4 (min) Glyphosate 8.122 8.175 8.066 8.1168.092 8.017 8.147 8.077 (%)* PMIDA (%)* 0.010 0.006 ND 0.002 0.002 0.0020.002 0.003 CH₂O (%)* 0.063 0.068 0.043 0.043 0.105 0.087 0.057 0.076HCO₂H (%)* 0.271 0.203 0.245 0.246 0.183 0.158 0.325 0.444 AMPA/MAMPA0.056 0.081 0.046 0.046 0.070 0.148 0.051 0.054 (%)* NMG (%)* 0.0250.014 0.018 0.019 0.024 0.004 0.016 0.020 Run No. 9 10 11 12 13 14Control Metal As₂O₃ As₂O₃ Mn₂O₃ Mn₂O₃ As₂O₅•3H₂O As₂O₅•3H₂O Added (60ppm) (120 ppm) (60 ppm) (120 ppm) (60 ppm) (120 ppm) Run Time 73.5 60.556.9 57 56.6 65.1 63 (min) Glyphosate 7.889 7.878 7.668 7.644 8.2748.409 8.198 (%)* PMIDA (%)* 0.101 0.396 0.002 ND 0.003 0.000 0.003 CH₂O(%)* 0.562 0.851 0.076 0.104 0.045 0.048 0.041 HCO₂H (%)* 0.365 0.5410.256 0.299 0.239 0.208 0.271 AMPA/MAMPA 0.085 0.066 0.113 0.094 0.0570.060 0.055 (%)* NMG (%)* 0.330 0.348 0.018 0.039 0.013 0.008 0.015*(mass ÷ total reaction mass) × 100%ND means none detected

Example 22 Evaluation of Silver, Cerium and Cobalt as SupplementalPromoters

Nine single-run oxidation experiments were conducted to determine theeffects of the one-time additions of tellurium, silver oxide, ceriumoxide, cobalt oxide and bismuth oxide salts to a PMIDA oxidationreaction.

The experiments were conducted using a catalyst containing 5% by weightplatinum and 0.5% by weight iron. Each experiment was carried out in a300 ml reactor (made of alloy metal, Hastelloy C, Autoclave Engineers)using 0.9 g catalyst (0.5% by weight of the total reaction mass), 21.8 gPMIDA (12.1% by weight of the total reaction mass), 1000 ppmformaldehyde, 5000 ppm formic acid, a total reaction mass of 180 g, apressure of 90 psig, a temperature of 100° C., and an agitation rate of900 rpm. The oxygen feed rate for the first 22 minutes was 141 cc/min.,and then 45 cc/min until the PMIDA was essentially depleted. In thecontrol experiment, no metal was introduced. In the other experiments,metal was added to the reaction medium as follows:

Experiment 1—0.013 g (60 ppm) of silver oxide (AgO) was added;Experiment 2—0.013 g (60 ppm) of cerium oxide (CeO₂) was added;Experiment 3—0.027 g (120 ppm) of cerium oxide (CeO₂) was added;Experiment 4—0.015 g (60 ppm) of cobalt oxide (CO₃O₄) was added;Experiment 5—0.030 g (120 ppm) of cobalt oxide (CO₃O₄) was added;Experiment 6—60 ppm of tellurium was added; Experiment 7—120 ppm oftellurium was added; Experiment 8—0.0616 g (60 ppm) of H₃BO₃ was added;and Experiment 9—0.1232 g (120 ppm) of H₃BO₃ was added.

Results (except for Experiment 1 which was ineffective) are shown inTable 20. TABLE 20 Exp. No. 2 3 4 5 6 7 8 9 Control Metal CeO₂ CeO₂Co₃O₄ Co₃O₄ Te Te H₃BO₃ H₃BO₃ Added (60 ppm) (120 ppm) (60 ppm) (120ppm) (60 ppm) (120 ppm) (60 ppm) (120 ppm) Run Time 45.7 44 43.7 44.629.4 29.5 47.8 44.6 44.5 (min) Glyphosate 6.529 8.030 8.042 8.055 7.7657.738 7.926 7.906 8.070 (%)* PMIDA (%)* 0.055 0.232 0.134 0.207 0.0120.009 0.090 0.120 0.127 CH₂O (%)* 0.071 0.072 0.085 0.093 0.783 0.8100.070 0.074 0.065 HCO₂H (%)* 0.409 0.432 0.422 0.438 0.039 0.040 0.2610.314 0.334 AMPA/MAMPA 0.035 0.030 0.033 0.033 0.061 0.062 0.037 0.0350.031 (%)* NMG (%)* 0.031 0.028 0.032 0.034 0.050 0.053 0.024 0.0260.031*(mass ÷ total reaction mass) × 100%“ND” means none detected

Example 23 Evaluation of Titanium as a Supplemental Promoter

Four single-run oxidation experiments were conducted to determine theeffects of the one-time addition of titanium oxide salt to a PMIDAoxidation reaction.

The experiments were conducted using a catalyst containing 5% by weightplatinum and 0.5% by weight iron. Each experiment was carried out in a300 ml reactor (made of alloy metal, Hastelloy C, Autoclave Engineers)using 0.9 g catalyst (0.5% by weight of the total reaction mass), 21.8 gPMIDA (12.1% by weight of the total reaction mass), 1000 ppmformaldehyde, 5000 ppm formic acid, a total reaction mass of 180 g, apressure of 90 psig, a temperature of 100° C., and an agitation rate of900 rpm. The oxygen feed rate for the first 22 minutes was 141 cc/min.,and then 45 cc/min until the PMIDA was essentially depleted. In thecontrol experiment, no metal was introduced. In the other experiments,0.018 g (60 ppm) of titanium (IV) oxide (TiO₂) was added to the reactionmedium in Experiment 1 and 0.036 g (120 ppm) of titanium (IV) oxide(TiO₂) was added to the reaction medium in Experiment 2. Results for theexperiments as well as the control experiment are illustrated in Table21. TABLE 21 Exp. No. 1 2 Control Metal Added TiO₂ TiO₂ (60 ppm) (120ppm) Run Time (min) 38.8 36.8 44.5 Glyphosate (%)* 7.812 7.787 8.070PMIDA (%)* 0.503 0.670 0.127 CH₂O (%)* 0.071 0.079 0.065 HCO₂H (%)*0.463 0.513 0.334 AMPA/MAMPA (%)* 0.027 0.027 0.031 NMG (%)* 0.023 0.0260.031*(mass ÷ total reaction mass) × 100%“ND” means none detected

Example 24 Evaluation of Vanadium, Gallium, Niobium, Tantalum Seleniumand Antimony as a Supplemental Promoter

Thirteen single-run oxidation experiments were conducted to determinethe effects of the one-time additions of vanadium oxide, gallium oxide,niobium oxide, tantalum oxide, selenium oxide, and antimony oxide saltsto a PMIDA oxidation reaction.

The experiments were conducted using a catalyst containing 5% by weightplatinum and 0.5% by weight iron. Each experiment was carried out in a300 ml reactor (made of alloy metal, Hastelloy C, Autoclave Engineers)using 0.9 g catalyst (0.5% by weight of the total reaction mass), 21.8 gPMIDA (12.1% by weight of the total reaction mass), 1000 ppmformaldehyde, 5000 ppm formic acid, a total reaction mass of 180 g, apressure of 90 psig, a temperature of 100° C., and an agitation rate of900 rpm. The oxygen feed rate for the first 22 minutes was 141 cc/min.,and then 45 cc/min until the PMIDA was essentially depleted. In thecontrol experiment, no metal was introduced. In the other experiments,metal was added to the reaction medium as follows:

Experiment 1—0.019 g (60 ppm) of vanadium oxide (V₂O₅) was added;Experiment 2—0.039 g (120 ppm) of vanadium oxide (V₂O₅) was added;Experiment 3—0.015 g (60 ppm) of gallium oxide (Ga₂O₃) was added;Experiment 4—0.029 g (120 ppm) of gallium oxide (Ga₂O₃) was added;Experiment 5—0.015 g (60 ppm) of niobium oxide (Nb₂O₅) was added;Experiment 6—0.031 g (120 ppm) of niobium oxide (Nb₂O₅) was added;Experiment 7—0.013 g (60 ppm) of tantalum oxide (Ta₂O₅) was added;Experiment 8—0.026 g (120 ppm) of tantalum oxide (Ta₂O₅) was added;Experiment 9—0.015 g (60 ppm) of selenium oxide (SeO₂) was added;Experiment 10—0.030 g (120 ppm) of selenium oxide (SeO₂) was added;Experiment 11—0.013 g (60 ppm) of antimony oxide (Sb₂O₃) was added; andExperiment 12—0.026 g (120 ppm) of antimony oxide (Sb₂O₃) was added.

Results for the experiments as well as the control experiment areillustrated in Table 22. TABLE 22 Exp. No. 1 2 3 4 5 6 7 8 Metal V₂O₅V₂O₅ Ga₂O₃ Ga₂O₃ Nb₂O₅ Nb₂O₅ Ta₂O₅ Ta₂O₅ Added (60 ppm) (120 ppm) (60ppm) (120 ppm) (60 ppm) (120 ppm) (60 ppm) (120 ppm) Run Time 41.1 35.939.3 41.5 43.8 42.8 42.6 41.0 (min) Glyphosate 7.200 6.981 8.082 8.1278.170 8.252 8.116 7.989 (%)* PMIDA (%)* 0.086 0.264 0.326 0.302 0.2210.191 0.303 0.380 CH₂O (%)* 0.153 0.172 0.080 0.076 0.074 0.068 0.0790.084 HCO₂H (%)* 0.552 0.579 0.483 0.448 0.421 0.411 0.438 0.461AMPA/MAMPA 0.214 0.252 0.028 0.030 0.032 0.030 0.029 0.029 (%)* NMG (%)*0.080 0.117 0.033 0.030 0.032 0.032 0.034 0.036 Exp. No. 9 10 11 12Control Metal Added SeO₂ SeO₂ Sb₂O₃ Sb₂O₃ (60 ppm) (120 ppm) (60 ppm)(120 ppm) Run Time (min) 84 61.4 58.1 61.2 43.0 Glyphosate 3.705 2.8488.096 8.191 8.076 (%)* PMIDA (%)* lg. peak lg. peak 0.020 0.201 0.251CH₂O (%)* 0.268 0.300 0.011 0.016 0.083 HCO₂H (%)* 0.434 0.523 0.0680.039 0.441 AMPA/MAMPA 0.035 0.022 0.054 0.054 0.031 (%)* NMG (%)* 0.0320.025 0.003 0.007 0.030*(mass ÷ total reaction mass) × 100%“ND” means none detected

Example 25 Evaluation of Lanthanum, Rhenium and Ruthenium as aSupplemental Promoter

Six single-run oxidation experiments were conducted to determine theeffects of the one-time additions of lanthanum oxide, rhenium oxide andruthenium oxide salts to a PMIDA oxidation reaction.

The experiments were conducted using a catalyst containing 5% by weightplatinum and 0.5% by weight iron. Each experiment was carried out in a300 ml reactor (made of alloy metal, Hastelloy C, Autoclave Engineers)using 0.9 g catalyst (0.5% by weight of the total reaction mass), 21.8 gPMIDA (12.1% by weight of the total reaction mass), 1000 ppmformaldehyde, 5000 ppm formic acid, a total reaction mass of 180 g, apressure of 90 psig, a temperature of 100° C., and an agitation rate of900 rpm. The oxygen feed rate for the first 22 minutes was 141 cc/min.,and then 45 cc/min until the PMIDA was essentially depleted. In thecontrol experiment, no metal was introduced. In the other experiments,metal was added to the reaction medium as follows:

Experiment 1—0.013 g (60 ppm) of lanthanum oxide (La₂O₃) was added;Experiment 2—0.025 g (120 ppm) of lanthanum oxide (La₂O₃) was added;Experiment 3—0.013 g (60 ppm) of rhenium oxide (ReO₂) was added;Experiment 4—0.025 g (120 ppm) of rhenium oxide (ReO₂) was added;Experiment 5—0.014 g (60 ppm) of ruthenium oxide (RuO₂) was added; andExperiment 6—0.028 g (120 ppm) of ruthenium oxide (RuO₂) was added.Results are shown in Table 23. TABLE 23 Exp. No. 1 2 3 4 5 6 ControlMetal Added La₂O₃ La₂O₃ ReO₂ ReO₂ RuO₂ RuO₂ (60 ppm) (120 ppm) (60 ppm)(120 ppm) (60 ppm) (120 ppm) Run Time 58.2 44 43.7 48.7 43.5 44.1 44.5(min) Glyphosate 7.960 8.041 8.120 7.921 7.939 7.978 8.070 (%)* PMIDA(%)* 0.235 0.208 0.268 0.245 0.193 0.193 0.127 CH₂O (%)* 0.082 0.0890.073 0.061 0.070 0.063 0.065 HCO₂H (%)* 0.356 0.350 0.391 0.376 0.4170.395 0.334 AMPA/MAMPA 0.040 0.041 0.035 0.036 0.034 0.036 0.031 (%)*NMG (%)* 0.034 0.037 0.028 0.028 0.029 0.027 0.031*(mass ÷ total reaction mass) × 100%“ND” means none detected

Example 26 Effect of Two Supplemental Promoters

A sixteen-run oxidation experiment was conducted to determine theeffects of the addition two supplemental promoters (bismuth followed bytellurium) for use in a PMIDA oxidation reaction.

The experiment was conducted using a catalyst containing 5% by weightplatinum and 0.5% by weight iron. The experiments were carried out in a1L reactor (made of stainless steel, Autoclave Engineers) using 3.75 gcatalyst (0.75% by weight of the total reaction mass), 60.5 g PMIDA(12.1% by weight of the total reaction mass), 500 ppm formaldehyde, 500ppm formic acid, a total reaction mass of 500 g, a pressure of 135 psig,a temperature of 100° C., and an agitation rate of 900 rpm. The oxygenfeed rate for the first 22 minutes was 468 cc/min., and then 125 cc/minuntil the PMIDA was essentially depleted. In the control experiment, nometals were introduced as a supplemental promoter.

In adding the supplemental promoter, 0.034 g (60 ppm) of Bi₂O₃ wascharged to the first reaction. After the 6th reaction run, 0.0375 g (60ppm) of Te(IV)O₂ was charged to the reactor and the remaining tenexperiments were evaluated. Oxidation results for the experiments areillustrated in Table 24. As shown in FIGS. 12 and 13, the addition ofthe second supplemental promoter, Te, reduced the time to complete theoxidation of PMIDA and reduced the amount of noble metal found insolution. Thus, the use of a second supplemental promoter is beneficialto increase the rate of PMIDA oxidation and to reduce the amount ofnoble metal leaching from the catalyst. TABLE 24 Exp. Run TimeGlyphosate PMIDA CH₂O HCO₂H AMPA/MAMPA NMG No. (min) (%)* (%)* (%)* (%)*(%)* (%)* 1 37.4 7.776 0.018 0.016 0.039 0.127 0.000 2 37.6 8.452 0.0140.015 0.037 0.104 0.000 3 45 8.382 0.008 0.016 0.038 0.122 0.000 4 40.48.460 0.006 0.019 0.042 0.123 0.000 5 44.8 8.399 0.007 0.015 0.040 0.0880.000 6 26.7 8.459 0.023 0.533 0.131 0.058 0.073 7 27.2 8.326 0.0000.445 0.070 0.068 0.039 8 26 8.258 0.000 0.386 0.057 0.071 0.031 9 27.88.274 0.014 0.599 0.059 0.057 0.037 10 26.6 8.294 0.000 0.435 0.0540.069 0.029 11 26.3 8.224 0.015 0.408 0.059 0.062 0.036 12 26.4 8.2700.013 0.389 0.055 0.066 0.033 13 28.6 8.279 0.023 0.462 0.056 0.0490.043 14 27.5 8.314 0.015 0.412 0.053 0.061 0.037 15 27.8 8.243 0.0200.454 0.052 0.060 0.042 16 27.4 8.294 0.016 0.430 0.055 0.063 0.042*(mass ÷ total reaction mass) × 100%

Example 27 Comparison of CO Chemisorption for Bi-Doped Catalyst

Several samples of the 5% Pt/0.5% Fe on carbon catalyst used in theabove examples were studied using CO chemisorption measurements todetermine the number of active sites. The catalyst samples analyzed weretaken from PMIDA oxidation reactions. The catalyst samples had beenpreviously used in from 6 to 35 previous reaction cycles with theaddition of a bismuth supplemental promoter. A sample of the samecatalyst run 6 times without the addition of Bi was used as a referencesample.

A Micromeritics ASAP2010C static chemisorption instrument was used tocollect the volume adsorbed versus pressure data used to determine theμmol CO adsorbed and the dispersion. The catalyst samples were weighedusing a Mettler AT261 analytical balance. Approximately 0.2500 gm ofsample was used in the chemisorption experiments. Standard 10 mm I.D.flow through sample tubes held the sample and quartz wool plugs aided inrestricting sample movement. The samples were degassed under vacuumovernight at 150° C. before analysis. Ultra high purity nitrogen gas wasused as the backfill gas. Analysis of these samples was performed usingthe ASAP 2010 unit 2 gas chemisorption instrument from Micromeritics.TABLE 25 Evaluation Method Task Gas Temperature Hold time Flow He RT to150 @ 30 5° C./min Flow He 120 to 30 @ 5 20° C./min Evacuation 30° C. 15Leak Test 30° C. Evacuation 30° C. 15 Flow H2 30 to 150 @ 15 10° C./minEvacuation 150° C. 10 Evacuation 150 to 30 @ 30 20° C./min Leak Test 30°C. Evacuation 30° C. 30 Analysis CO 30° C.

TABLE 26 5% Pt/0.5% Fe Chemisorption Results CO chemisorption Sample ID(umol CO/gm cat) Dispersion (%)  6 runs w/o Bi 19.6 7.6  6 runs w/Bi 7.63.0 20 runs w/Bi 11.8 4.6 35 runs w/Bi 7.5 2.9

The CO chemisorption results showed a decrease in the amount ofadsorption in the samples treated with Bi when compared to a samplewhich had not been treated with Bi. The Bi treated samples had a COchemisorption as low as 7.5 μmol CO/g catalyst. The untreated sample hada CO chemisorption of 19.6 μmol CO/g catalyst.

Example 28 Effect of the Simultaneous Addition of Two SupplementalPromoters

Seven single-run oxidation experiments were conducted to determine theeffects of the simultaneous addition of two supplemental promoters(bismuth and tellurium) for use in a PMIDA oxidation reaction.

The experiments were conducted using a catalyst containing 5% by weightplatinum and 0.65% by weight iron. The experiments were carried out in a1L reactor (made of stainless steel, Autoclave Engineers) using 2.5 gcatalyst (0.5% by weight of the total reaction mass), 60.5 g PMIDA(12.1% by weight of the total reaction mass), 1000 ppm formaldehyde,5000 ppm formic acid, a total reaction mass of 500 g, a pressure of 110psig, a temperature of 100° C., and an agitation rate of 900 rpm. Theoxygen feed rate for the first 22 minutes was 392 cc/min., and then 125cc/min until the PMIDA was essentially depleted.

The experiments included adding supplemental promoter to the reactionmedium as follows:

-   -   1. No supplemental promoter was added in Experiment 1 as to        establish a baseline with the above catalyst;    -   2. 0.0075 g (12 ppm) tellurium dioxide was added in Experiment        2;    -   3. 0.0075 g (12 ppm) tellurium dioxide and 0.0067 g (12 ppm)        bismuth oxide were added in Experiment 3;    -   4. 0.015 g (24 ppm) tellurium dioxide was added in Experiment 4;    -   5. 0.015 g (24 ppm) tellurium dioxide and 0.0067 g (12 ppm)        bismuth oxide were added in Experiment 5;    -   6. 0.030 g (48 ppm) tellurium dioxide was added in Experiment 6;    -   7. 0.030 g (48 ppm) tellurium dioxide and 0.0067 g (12 ppm)        bismuth oxide were added to Experiment 7.

Results are shown in Table 27. TABLE 27 Exp. Run Time Glyphosate PMIDACH₂O HCO₂H AMPA/MAMPA NMG No. (min) (%)* (%)* (%)* (%)* (%)* (%)* 1 38.38.030 0.014 0.043 0.437 0.042 0.031 2 64.9 8.270 0.014 0.041 ND 0.0650.005 3 64.3 7.920 0.017 0.030 ND 0.067 ND 4 42.7 8.130 0.021 0.4650.057 0.084 0.055 5 35.3 7.790 0.008 0.504 0.052 0.072 0.039 6 37.48.160 0.011 0.553 0.073 0.097 0.073 7 30 8.140 0.029 0.560 0.065 0.1270.047*(mass ÷ total reaction mass) × 100%ND = “not detected”

Example 29 Effect of a Supplemental Promoter on the Catalytic Oxidationof Formic Acid and Formaldehyde

Two single-run oxidation experiments were conducted to determine theeffects of a supplemental promoter for use in the catalytic oxidation ofan aqueous stream of formic acid and formaldehyde.

The experiment was conducted using a catalyst containing 5% by weightplatinum and 0.5% by weight iron. The experiments were carried out in a300 ml reactor (made of alloyed metal, Hastelloy C, Autoclave Engineers)using 0.28 g catalyst, 5800 ppm formaldehyde, 3800 ppm formic acid, atotal reaction mass of 180 g, a pressure of 100 psig, a temperature of100° C., and an agitation rate of 900 rpm. The oxygen feed rate was 100cc/min.

The experiment consisted of three single-run oxidation experiments runfor 35 minutes each. Samples were collected and analyzed for In thefirst experiment, the aqueous formic acid and formaldehyde werecatalytically oxidized with no supplemental promoter added, so as toestablish a baseline. In the second experiment, 30 ppm of bismuth wasadded as a supplemental promoter and, in the third experiment, 30 ppm oftellurium was added as a supplemental promoter. Comparisons of theformic acid and formaldehyde destruction from the addition of bismuthand tellurium are shown in FIGS. 14, 15, 16 and 17.

The present invention is not limited to the above embodiments and can bevariously modified. The above description of the preferred embodiment isintended only to acquaint others skilled in the art with the invention,its principles, and its practical application so that others skilled inthe art may adapt and apply the invention in its numerous forms, as maybe best suited to the requirements of a particular use.

With reference to the use of the word(s) “comprise” or “comprises” or“comprising” in this entire specification (including the claims below),Applicants note that unless the context requires otherwise, those wordsare used on the basis and clear understanding that they are to beinterpreted inclusively, rather than exclusively, and that Applicantsintend each of those words to be so interpreted in construing thisentire specification.

1. A process for oxidizing a substrate selected from the groupconsisting of N-(phosphonomethyl)iminodiacetic acid or a salt thereof,formaldehyde, and formic acid, the process comprising contacting thesubstrate with an oxidation catalyst in the presence of oxygen, whereinthe catalyst comprises a carbon support having a noble metal, iron andcobalt at a surface of the carbon support, the noble metal beingselected from the group consisting of platinum, palladium, ruthenium,rhodium, iridium, silver, osmium, gold and combinations thereof.
 2. Aprocess as set forth in claim 1 wherein the catalyst comprises metalparticles comprising said noble metal at a surface of the carbonsupport.
 3. A process as set forth in claim 1 wherein the noble metalconstitutes from about 2.5 to about 10% by weight of the catalyst.
 4. Aprocess as set forth in claim 1 wherein the noble metal constitutes fromabout 3 to about 7.5% by weight of the catalyst.
 5. A process as setforth in claim 1 wherein the noble metal is platinum.
 6. A process asset forth in claim 1 wherein the carbon support is activated carbon. 7.A process as set forth in claim 1 wherein the contacting is conducted ina continuous reactor system.
 8. A process as set forth in claim 1wherein the contacting is carried out at a pressure of from about 30 toabout 130 psig.
 9. A process as set forth in claim 1 wherein thecontacting is carried out at a temperature of from about 80 to about110° C.
 10. A process as set forth in claim 1 wherein the contacting iscarried out in a solution or slurry having a pH of less than
 7. 11. Aprocess as set forth in claim 1 wherein the contacting is carried out ina solution or slurry having a pH of less than
 3. 12. A process as setforth in claim 1 wherein the contacting is carried out in a solution orslurry having a pH of from about 1 to about
 2. 13. A process as setforth in claim 1 wherein the substrate comprisesN-(phosphonomethyl)iminodiacetic acid or a salt thereof.